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