Arc Raiders has a boatload of materials for you to loot topside, and while most of them say what they're used for, Rusted Tools certainly do not. They're considered a rare recyclable material, and that's likely what you've done if you've found some already, and now you're frantically searching for more upon the grave realisation that Rusted Tools are actually vital in upgrading your Gunsmith.
The good news is that, at least right now, the Gunsmith II upgrade is the only use for Rusted Tools outside of recycling them for scrap metal, and you'll only need three of them. So, here's where you need to look to find Rusted Tools.
