Anybody tried a product called Micro-Mesh?
https://www.micro-surface.com/default.cfm?page_id=200
I've got nothing to gain by plugging them, but this stuff is well-known in modeling (cars, planes) circles. The regular stuff is great for plastics, and will produce an almost optical-quality finish.
Their "grits" go down to 12000 (twelve thousand), although I believe they go by a different set of standards than regular W or D sandpaper. The 12000 has the feel of leather, very smooth.
The backing is cloth instead of paper and it's very durable. You can also buy them with foam pads attached, which makes wet-sanding by hand easier.
I used the stuff to polish some scratches and a stain out of the clear instrument panel bezel and it looks brand new.
They have a kit for doing headlights, but I prefer to buy the larger sheets individually. They also sell different types of sheets for polishing aluminum and stainless steel.
Anyway, I just thought I'd point out this source in case no one else had tried it.