You could try your local Chevy Dealer, especailly if you know of one who deals in larger trucks. The part is most likely dis-continued, but it still may be on some old books. If you can get someone there with a little patience, he may have the answer for you. GMC should be the same and you may have better luck calling an old GMC dealer.
If that doesn't work out, you may want to go with a good used one. Preferably one with lower mileage.
