1. Go to workshop
2. Choose "Craft Items, Produce Ammo" (First one)
3. Go to "Thrown & Placed Decoys"
4. Choose "Craft Firecrackers" (5 firecrackers for 15 parts with perk Knowledge of Chemistry)
5. Craft them
6. Go to supply locker
7. Choose firecrackers and salvage them (This will give you 25 parts for 5 firecrackers)
+10 parts for 1 craft. The more firecrackers you craft, the more parts you will get. Repeat this with larger and larger quantities, and you will quickly accumulate a lot of parts. Profit.

You need to have a character with perk Knowledge of Chemistry, so you can craft 5 firecrackers, and not 3, so you can make it work on Dread difficult and higher. Without this perk you will craft 3 firecrackers for 15 parts, and dismantling 1 gives 5 parts, so it won't work.