You can also find regular assorted size steel rivets on line. I purchased a box of 100 a while back on Ebay. This has always been a problem with GM light duty trucks and cars. For the life of me I cannot figure out why they snap off while driving. When we were all kids it was a cheep fix not so now hub caps get a premium price. Let me check if I can find them and I will send you some. Kades51 has a good suggestion. I think the 37 had a 16" , which was called an artillery wheel due to the slots around center. they used the same hardware. Doc.

Currently making 1954 3100 better than new and Genetics