Only place I know to find them would be a junk yard.

I just saw a set of 4 on an AD Chevy rear axle in a junk yard last weekend, looked like it had been there for a looong time, doubt they even know they have them.
If you call, and they can't find them, have them check on the side of the hill behind the crusher with a bunch of other old tires.
G&G Auto Recycling in Winchester VA, 800-368-0854
This is their website, but not working right now, it was last week. http://www.gandgautorecycling.com/Contact_Us/contact_us.htm

Unless you are looking for a stock restoration I would use 19.5" wheels and tires.

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-