Micro-Surface makes the finest sandpaper around: Micro-Mesh abrasives. I originally used their sanding pads to get a perfect finish on a plastic model car by sanding each layer of spraypaint I applied to the model. Their finest sandpaper is rated at an incredible 12000 grit. (Although that number isn’t using the same ANSI scale as commonly available sandpaper).
I was amazed that I was able to sand a scratched plastic window to perfect clarity, although I shouldn’t have been surprised: micro-mesh is used to repair the acrylic windows used on many airplanes. I’ve since used the same hobby kit for repairing scratches in the clear coat of my REAL car. I’ve even carefully polished out deep scratches in the bottom of several CDs. You can also polish out scratches on reading glasses.
Micro-Surface makes a wide variety of abrasives, in every size and type I can imagine needing.