There are headlight lens 'refinishing' kits like below on the market:
http://www.eastwood.com/headlight-refinishing-kit.htmlJust about every wax or polish vendor makes them. You should be able to find 3 or 4 type kits in your local parts house.
While they do a decent job of clearing the haze and helping with the discoloration, you'll find that a car that's used, or stored outside will soon have hazy, yellowed lenses again in less than a year. I'd probably clean what you have, just so you can use the car, but look for NOS, or lightly used replacements. You may be able to fit ones off a newer model and maybe even still find them at the dealer, although they're probably not cheap.
