There are a number of various sanding shapes and tools available. Try searching "sanding" or similar at Micro Mark.
Many times I just make a sanding stick that will do a specific job. Recently I had a frame with ejector pin marks and raised text to be removed in small flat areas . .a common problem. The ejector pin recessed areas were filled and I made a sander using a paper punch, sandpaper, a wood dowel and double stick foam used for wall hanging. It should be obvious how these were put together, I believe. This principal works for many areas not accessible to common sanding sticks.