Where do you farm rusted gears in arc raiders?

Anything mechanical. Toolboxes, workbenches, the little industrial crates in garages and maintenance rooms, and scrapping junk items that list it as a component. The thing people miss is you don't have to find them as a drop, a lot of the dead weight loot you'd normally leave behind recycles into rusted gear back at base, so pick up the broken tools and old motors instead of skipping them.