I can find 19.5" tires, its the 10 lug wheels I want and like scott says, you gotta make sure they fit over the drums, I don't see why they won't if 20 inch rims fit over the drums with room to spare. I have seen them on ebay, but I'm not gonna spend $600 bucks without a test fit.
Scott, you tried late model 19.5" 3500HD rims and they didn't fit over the rear drums? Do you have a 2 speed rear end?