Since with Reforced some items were moved to other locations, so I started to write some notes for myself with the new locations of the pieces for the Remnants of the Old and The Windwall Way, and then this sort of guide evolved from there...
I hope it can help someone in trouble finding some missing item(s)... and it goes with saying:

WARNING, SPOILERS AHEAD!!!

First things first, in Reforced it's not Isgrimm who craft the artefacts for you anymore!
Now at Mulandir: Nexus, near Isgrimm, you will find a nice crafing table for all your needs.

About this guide, I will write them as I found them - in the same order as I played and found/grabbed the artefact, meaning that the first Greyfell section is about the first time I was there and the second one is about the second time I was there after coming back from Liannon... and so on...
In fact, some locations are marked later than when I was there first because that's when I went back to grab the artefact...
For example, Farlorn's Hope is placed in this guide after Mulandir because it's only then that those items are available there, specially one that is required to get another artefact later.
This is by no means a guide on which order you should go to each location!

Unfortunatly, since I wanted to edit the screenshots to better display where each item is, I couldn't use ingame screenshots through Steam and the images had to be downsized in order to fit the maximum allowed size.
I'm sorry about that... I might update this also with link to the good quality images.

Edit 20/08/2023: Finally was able to fully port this guide to the SpellForce Wiki - Rohens encyclopedia AND not only with high quality images but also with better styling to make it easier to find what you're looking for: Spellforce 3: Reforced - Artefacts Locations [wiki.spellforce.info]

Notes and clarification on Bartering 3 -- Thank you, Crux2 for you comment that remind me of including this note.

After your first visit to The Eye and upon its completion, your Avatar will have access to 3rd level abilities.
Bartering 3 is the third level of said ability in the Leadership ability tree and will give you access to a hidden tab on ALL Merchants' Inventory.

• Greykeep: Grey Tower
  Chest in the room of the alchemist Albertus DeRhemyes
  
  Mage's Note - Vision [Eye of the World]

• Mother Calia's Refugee Camp
  Crate
  
  Master of Life and Death - Knob
• Pillar of the Fallen
  Northside of the river to East, near some undead, Light it up
  
  Impervious Protector
  (Chest spawns on the third pillar lit)
  

• Greykeep: Prison
  
  Bag, right before the Southeastern exit
  
  Old Mysterious Page II [Ring of the Mystics]
  
  
• Pillar of the Fallen
  Southeastern corner, Light it up
  
  Impervious Protector
  (Chest spawns on the third pillar lit)
  

• Lathweyn - River Bed
  Corpse
  Executioner's Blade - Hilt
  
  
• Shrine outside Human Camp
  Corpse
  Shield of Benediction - Inner Plate
  
• House south of Lathweyn
  Bag
  Old Mysterious Page I [Ring of the Mystics]
  
• Northwestern path
  Chest
  Elven Token [King Ayelith's Oath]
  
• Southeast, Shrine of Barga Gor
  Elven Tormented Soul
  Guardians' Grace - Padding
  

NOTE: You can explore the total of Mulandir outside the Nexus as soon as you complete one of the quests from Gaining Allies.

---

• Northern Godstone
  Chest nearby
  
  Dwarven Outer Armor Plating [Isgrimm Armor]
  
  
• Northwest from Northern Godstone
  Dead Body
  
  Hammer of the Smith - Head
  
  
• Northeast from Godstone North from Western Ghost Watchers
  Bag
  
  Master of Life and Death - Hilt
  
  
• West from Southwestern Godstone
  Half-buried corpse
  
  Axe of the Mountains - Knob
  
• Southwest from the central square, Northeast from the Southern Godstone
  Pillar (Requires one Golem's Core)
  
  Golem's Heart
  

• Farlorn's Hope: Amethyst Cave
  Skeleton
  
  Rol'Gar's Skull [Berserker Armor]
  
• Old Orc main camp
  Bag at a small path up to Northeast from Zenrakk
  
  Greataxe of the Chieftain - Bottom of the Head
  

• Foot of Barga Gor: Caverns
  Dead body, middle of the map
  
  Call of the Forest - Top Plate
  
  
• Northwest of the northern Godstone
  Bag, under a stone archway
  
  Executioner's Blade - Tip of the Blade
  
  
• Northwest of Kae-Ran Cal'Rak
  Barrel
  
  Orcish Token [King Ayelith's Oath]
  
• Up North, West from sacred fighting area
  Bag
  
  Shield of Benediction - Handle
  
• Zor'Gar's cave
  Zor'Gar
  
  Berserker Armor
  NOTE: You can get it on your first visit at this map IF you go to Farlorn's Hope: Amethyst Cave while doing The Refugees quest before the Power Struggle here, otherwise you'll have to come back later... but before visiting The Eye for the first time.

• Berghol the Bodacious
  After his recruitment in the Foot of Barga Gor
  
  Reinforced Adamantium Slab [Isgrimm's Armor]
  
• Ulfric, Rorik's brother
  The dwarf Merchant near Isgrimm, available after the 1st visit to Aonir's Blade IF you completed his quest
  
  Dwarven Token [King Ayelith's Oath]
  NOTE: Since when I played the game to write this guide, player ColdFrost reported in the comments that the Dwarven Token also requires Bartering 3.
  
  Lich's Demise Require Bartering 3
  
  
• Chest near the Orc faction
  Only reachable after the Orcs upgraded their Cal'Rak to its maximum
  
  Reinforced Dwarven Shoulder Pads [Isgrimm Armor]
  

• Pillar of the Fallen
  near the Godstone South of the Purity Camp, Light it up
  
  Impervious Protector
  (Chest spawns on the third pillar lit)
  
  
• Western bridge
  Corpse in the river bed nearby
  
  Greataxe of the Chieftain - Haft
  

NOTE: Exceptionally at Everlight, I'm writing ALL items I found here, although some of them I had to come back at later times to grab them because some require items found on latter locations, and some require to do some quests to get access to certain places.

---

• West side of the City
  Blacksmith (Merchant) near Vilron
  
  Pride of Nortander - Padding
  
• Merchant Area
  Alchemist
  
  Lavender Perfume [Ring of the Sacred Rite]
  
  
• North Gate to the City
  Corpse up North, near River outside East side of town
  
  Shield of Benediction - Outer Plate
  
  
• Creators' Guild island
  Half-buried crate on the Eastern shore
  
  Decorative Armor [Gift of the Giants]
  
  
• Fields on the East
  Shrine to the northeast next to the fields - Requires both [Decorative Armor] and [Decorative Sword]
  
  Gift of the Giants
  
• Southern Coast
  The Referee, spawn from the statue on the southern coast - Require [Duelist's Sword] and [Duelist's Gloves]
  
  Thrill of the Duel
  
• Everlight: Creators' Guild
  Satchel, upper floor, westside
  
  Mage's Note - Self-awareness [Eye of the World]
  
  
• Everlight: Slaughterhouse
  Crate near the Butcher
  
  Duelist's Gloves [Thrill of the Duel]
  
  
• Everlight: Slaughterhouse
  Locked Chest, Requires the 3 Mage's Notes
  
  Eye of the World
  
  
• Everlight: Hideout
  Corpse
  
  Pride of Nortander - Bottom Plate
  
  
• Everlight: Hideout
  Bag
  
  Duelist's Sword [Thrill of the Duel]
  
  
• Everlight: Glittering Mine
  Corpse
  
  Executioner's Blade - Body of the Blade
  
  
• Everlight: Glittering Mine
  
  Shrine of Barga Gor, Miner's Tormented Soul
  
  Guardians' Grace - Bottom Plate
  
  
• Everlight: Sewers
  Falar (You need to spray him with [Lavender Perfume] to wake him up)
  
  Ring of the Sacred Rite
  

• Western beach
  corpse surrounded by small rocks
  
  Greataxe of the Chieftain - Knob
  
  
• Medusa Fortress
  Northeast, next to the eastern tower
  
  Sword of the Renegade - Hilt
  
  
• Serpent Altar, hill above Hybernian Temple
  Eternal Chanter, spawns by inserting all serpent stones
  
  Shield of Deadly Allure
  

• Southwest Plateau
  Ritual Circle, Tribe-Eater
  
  VAT Fragment of the Phoenix [Shield of the Phoenix]
  NOTE: If you decide to sacrifice your men to calm the demon, then the Tribe-Eater won't appear and you will not be able to get the Shield of the Phoenix.
  
• Southwest Plateau
  Corpse, North of the Ritual Circle
  
  Greataxe of the Chieftain - Top of the Head
  

Attention: You won't be able to return to the Laboratory again, so make sure not to miss anything while in there. or it will be lost forever.

---

• The Eye: Isamo's Laboratory
  Crate inside Eastern hidden passage (press a wall face statue)
  
  Final Heartbeat
  
• The Eye: Isamo's Laboratory
  Corpse inside Eastern hidden passage (press a wall face statue)
  
  Dwarven Skull Padding [Isgrimm Helmet]
  
  
• The Eye: Isamo's Laboratory
  Western hidden passage (press a wall face statue), just before meeting Helena's ghost
  
  Final Breath
  
  
• The Eye: Isamo's Laboratory
  Library (MUST HAVE [Old Mysterious Page I] and [Old Mysterious Page II] in your inventory)
  
  Ring of the Mystics
  

• Rude Awakening attack
  East, The Bane attack, Liliath
  
  Liliath's Key [Defilers' Bane]
  NOTE: I can't remember for what this key is needed, if for anything...
  If anyone knows, please let me know in the comments...
  
• Rude Awakening attack
  Northwest, The Lightbringers attack, High Lightbringer Matthew(?)
  
  Secret of the Pure [Purifying Shield]
  

• Fortress
  Crate to the left from High-Keeper Arenor
  
  ION Fragment of the Phoenix [Shield of the Phoenix]
  
  
• Fortress
  Crate to the right from High-Keeper Arenor
  
  Empyrian Leather Shoulder Pads [Isgrimm Armor]
  
  
• Shrine of Salvation
  Southeastern Plateau - Requires the three Fragments of the Phoenix
  
  Shield of the Phoenix
  

• Hybernian Temple
  Northwest, Bag just before the titan scrolls' table
  
  Master of Life and Death - Blade
  

• Southeast Corner
  Edun Darrel (Merchant)
  
  Might of the Giants - Haft
  Hammer of the Smith - Haft Require Bartering 3
  
  
• Small path north from the middle bridge/dam
  Corpse (you might have to turn the camera to find it)
  
  Axe of the Mountains - Head
  
  
• Shrine of Barga Gor
  Hybernian Tormented Soul
  
  Guardians' Grace - Top Plate
  
  
• Eastside, up North from the Northern bridge
  Corrupted Bear (Rhonivarsh)
  
  Rhonivarsh's Claw [Van'Karewa]
  
  
• Dried part of the dam North from the miasma
  Wyvern (Queen of the Skies)
  
  Wing of the Queen of the Skies [Van'Karewa]
  
  
• Westside, Purity of Light Main Camp
  High Lightbringer Mark
  
  Secret of the Pure [Purifying Shield]
  
  
• Southwestern hybernian ruin
  Corrupted Spider (Arach)
  
  Arach's Fang [Van'Karewa]
  
  
• Altar at the dried out area south of the dam
  Requires Rhonivarsh's Claw, Wing of the Queen of the Skies and Arach's Fang
  
  Van'Karewa
  
  
• South of the middle bridge/dam inside the dried river
  Crate
  
  Lich's Mask
  

• Southeast
  Satchel on the table outside Raith's hut
  
  Mage's Note - Perseverance [Eye of the World]
  
  
• East border
  Corpse near a empty barrel on the cliff
  
  Axe of the Mountains - Haft
  
  
• West from first Godstone, Former Tomb of House Leonidar
  Require [Leonidar Insignia Ring]
  
  Armor of the Mage
  

• North from your Main Camp
  Locked Chest (Requires Dexterity 9 from the one who opens it)
  
  Brand of the Hunter
  
• Middle Purity Camp near hidden tunnel
  High Lightbringer Luke
  
  Secret of the Pure [Purifying Shield]
  
  
• Shrine of the Pure
  North of the middle gate, North of the wall - Requires three Secrets of the Pure
  
  Purifying Shield
  
  
• Northeastern corner, inside previously closed border
  Corpse
  
  Call of the Forest - Rune
  

• Lake at the Oasis
  Bag near the lake next to some Fish hanging on a drying rack
  
  SAL Fragment of the Phoenix [Shield of the Phoenix]
  
  
• Lake at the Oasis
  Dead body East from the Godstone near the lake
  
  Might of the Giants - Bottom of the Head
  
  
• Eastern border
  Half-buried Chest on a small passageway South from the Eastern Godstone
  
  A Slab of Dwarven Moonsilver [Isgrimm Armor]
  
  
• Northwest
  Dead body surrounded by some spiders
  
  Call of the Forest - Bottom Plate
  

• Middle Northern sector
  Bag, next to a sitting dead body leaning to a shack
  
  Human Token [King Ayelith's Oath]
  
  
• Northeastern village
  Crate under a tree - Requires [Liliath's Key]
  
  Defilers' Bane
  
• Altar of Hirin, up hill behind the Titan's Altar
  Requires 50 units of your faction's magic resource (Arya, Lenya or Black Ash)
  
  Dreamweaver's Elegy
  
  
• Western Border
  Dead Body under a tree near a lake
  
  Might of the Giants - Top of the Head
  
• Southeastern Undead Fortress
  Bag, North of the fortress to the southwest with the undead bandits (You will need to rotate the camera slightly to see it)
  
  Pride of Nortander - Top Plate
  
  
• Southeastern Undead Fortress
  Crate near a statue, Southwestern corner to the east path around the undead bandit castle.
  
  Decorative Sword [Gift of the Giants]
  
  
• Eastern Quarry turned Prison
  Crate next to a house north from where Tristam is imprisoned
  
  Dwarven Inner Armor Plating [Isgrimm Armor]
  

• King Ayelith's statue to the north
  Requires Orc, Dwarven, Elven and Human Token
  
  King Ayelith's Oath
  

• Eastern border
  Bag next to some boxes, West from the Deserter
  
  Discarded Dwarven Plate Mail [Isgrimm Armor]
  
  
• Eastern border
  Bag outside the house near the Deserter
  
  Sword of the Renegade - Blade
  
  
• Northern altar
  The 3 undead must be killed inside the sphere of light to summon the chest
  
  Soulreaver
  
  
• Isamo's Laboratory entrance
  Amaria Leonidar
  
  Leonidar Insignia Ring [Armor of the Mage]
  

• Greykeep: Hall of War
  Masked Priest (Dreamweaver)
  
  Treasure Key [Hex Protector]
  
  
• Greykeep: Undercroft
  Treasure Room
  
  Hex Protector
  
  
• Pillar of the Fallen
  If you light it up again when going there for the (Optional) Kill the guards in the courtyard quest, you'll get a 2nd one.
  (Probably a Bug! Might be fixed at some point in the future but it's been here since Legacy, so...)
  
  Impervious Protector
  

I also tried to give the location where some others artefact level items can be found... but I might have to update later on to complete this part, specially with the new items Reforced added to the base campaign...

Meanwhile, if you find any artefact item that is not mentioned here and want me to add it, leave a comment with its name and location and I'll include it when updating it.

Also, English is not my primary language so, please report any mistakes I might have made in the comments.

Thank you and I hope this little guide can be useful.

Update 14/7/2022

• Added the [Defiler's Bane] with the [Liliath's Key] connection, thanks to CUMfucius comment.
  
• Added the Alchemist (merchant) location in Everlight, from whom you can buy the [Lavender Perfume] required to wake up Falar in order to loot the [Ring of the Sacred Rite]

Update 28/9/2022

• Added section Mulandir, Nexus to include the Reinforced Adamantium Slab for [Isgrimm's Armor] - Thank you, Gerwant Z Libii

Update 03/4/2023

• Added section [Golem's Heart] at Mulandir - Thank you, ColdFrost for the sugestion and to games_fan17 for providing the screenshot

Update 20/8/2023

• Added a link to the wiki article with this same guide BUT with better images in the Introduction section
  
• Added a Note about Bartering 3 in the Introduction section - Thank you, Crux2 for your comment about it.

https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=2893654684