Goodyear makes a 37" tire for a 15" wheel. They make the MTR now in that size. They used to make the GSA in that size. You might be able to find some used GSA's.
Goodyear still makes the GSA in a 37 x 15. I ran that same tire at Henderson on my 8 truck and didn't have 1 flat. Goodyear also has the MTR in a 37 x 15.