I have never bought one, but if I were to start looking for one I would look at auto auctions. I would also ask body shops and dealers because they probably know where to get one. Body shop is perhaps the best bet, and tell them to keep you in mind if they see the model you are looking for. Yoy could even talk to local insurance companys and have them call you if somebody wrecks one like you are looking for.
Good luck
Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-