I polish celluloid all the time and I have two methods that are safe and will make them look as good as new.

The first is get a can of cape cod polishing cloths, you can get them on Eboy. Just some light rubbing and they do a fantastic job. The other uses a dremmel with a muslin buff and some yellow rouge designed for very soft metals and plastic. You just apply the rouge to the muslin and using low speed, little pressure and keep moving rapidly at all times until it polishes then repeat with a chamois wheel. I got the rouge off the tool shop at timezone.com.

Personally I think the cape cod cloths are best unless the scales are really chewed up then the dremmel is better.