Direct answer: Simple Gun Parts in ARC Raiders are not craftable and must be obtained through looting, recycling, or buying from Celeste’s shop using Assorted Seeds. They are used as ingredients to craft other gun parts and weapons, and you can often find them from smaller ARCs like Hornets and Wasps, as well as in weapon caches and military-style loot spots. Focus on farming these sources and then use Blueprints and Refiner II to assemble the more advanced gun parts you need.