I don’t understand what you mean by old Roblox guns, there are many free assets online that have guns with separated parts such as on TurboSquid, if you find a gun you like, you can try separating it on Blender and uploading it.
i mean those like gears of roblox, and yes i know i can go to blender and separate the only problem is that i am worried that i am going to get banned for re-uploading assets