AFIM S1960 can be located in Arizona - Coconino area and it can be unlocked by completing the mission "Out of the dirt", this can be done by towing it back into the marker near camping site (spawn). It's quite straight forward, but requires some pulling power. Watch the video for detailed route.

ANK MK38 Civilian is located in Carpathians - Mountain Labyrinths region and it can be unlocked by completing the mission "Right person for right job", which requires you to tow the ANK MK38 back to western camp site. Check the video for detailed route.

You can unlock this truck by completing the mission "Unsuccessful Geoanalysis" which is located in Arizona - Grand Canyon region.
Here's a detailed video that shows and explains how to complete the mission.

Khan 39 Marshall can be unlocked by completing the mission "Where trucks dare not tread" which is located in Carpathians - SlipRock Swamps region. it's very easy and fast mission and details can be seen on the video below.

Khan Lo4F (veggie loaf) can be found in Arizona - Grand Canyon region and it should be first vehicle you unlock. You can unlock it by completing the mission "Unfortunate trip", where you have to tow it back to base camp. Watch the video for detailed route and location.

KRS 58 Bandit can be found in Arizona - Sonoran Desert region and you can unlock it by completing the "Quicksand" mission, where you have to tow the KRS 58 Bandit across half the map. Watch the video for detailed route.

It can be found and unlocked on the Kanab Creek map. it's main expedition mission, but i wanted to include it anyways to complete the unlocking guide, this shows you exact method on how to unlock it.

It's rather easy, except one part that makes it hard. You need to tow it thru ford with high flow and that can be tricky. BEST mud tires are requirement or you'll end up getting stuck. Watch the video to learn details on how to do it.

Tatra Force T815-7 can be found in Carpathians - SlipRock Swamps region and you can unlock it by completing the mission "Attempt to ford the river", which can be accepted in 3 places, one of them is right next to the vehicle and one is next to northern outpost garage.
Check the video below for details on how to get it to its destination.

Tatra 805 can be found in Arizona - Wahweap bay region and you can unlock it by completing the mission "raining cars", which can be done by towing the Tatra 805 back to the marker near base camp. Check the video for detailed path.

TUZ 108 WARTHOG can be found in carpathians region and you can unlock it by completing the "Logistics issues" mission, which is quite easy. You have to tow TUZ 108 Warthog back to camp site, watch the video for detailed route and location.

YAR 87 can be unlocked by completing the mission "Lost in the Hills", watch the video below for detailed location and route.