In this video guide I will show you how you can install 5 modifications of each category on a single weapon. Now to find the parts for these they will just be scattered around the wasteland on dead bodies or the enemies that you kill. Just be sure to hold the B button on the weapons so you take all the accessories on them. And don't forget to LOOT EVERYTHING to help find more items. Once that is done either go to a safe house with a workbench or go into your backpack and go to your weapons and start installing the mods.