the dennis kirk catalog sells NOVUS plastic restoration kit.there is also one more product on the market but i cant think of the name. their both 3 step processes that are a pain in the***. but with a little work they come out pretty good.
YZ, My brother took some car wax and a wheel buffer and made my WHOLE bike look like new. He used a wheel buffer, not and orbital. I am really impressed. I didn't have to buy anything and it is easily redone. :D
If they are surface scratches, try a heat gun or hair dryer. They will take out the discoloration due to scratches and bends. It can make deep ones look better, but still have the scratch.