1937 oliver hart parr 70

I'm in desperate need of help with my row crop 70. Some of these came with 38 inch rear tires, and some came with 40 inch rear tires. I have the one that came with 40 inch tires. They don't make them anymore. I either need new 38 inch rims that will fit my wheels, or to find someone that has a 40 inch tire laying around. Another idea I had, is there anyone that makes specialty tires. Other than the tire issue, it's a sweet running tractor. I'd like to make the labor day tractor show this year with it, if possible