Eastwood company sells a headlight polishing kit. What it consists of is a tube of Autosol Metal Polish, and a polishing wheel/buffer for your drill.
Yes, it really works. Yes it'* metal polish. Yes it works on gun parts, too.
Anyhoo, I've used it on a friend'* 1994 Lincoln Town Car, with pretty good results. The old headlight looked pretty close to the new one (1 was replaced after an accident). And, they were plastic headlights.
So, if you can find Autosol somewhere, snagit. Stuff works well. Used it on my sword, guns, headlights, etc...