Well, you could always try Ebay or maybe find one on Craigslist if your lucky. If you cant find it, try Classic Industries. If nowhere has it, just go to the junk yard and see if they have it. Is it dented or rusted out? Cause if you cant find the part, you could always just vacuum it out with suction if its dented. and if rusted, just cut out the bad piece of medal and then replace, or just sand it down and use fiberglass or bondo to refill.
Hope this helps