A 16" Ford 3/4 ton wheel will work. Dexstar trailer wheels are patterned after the Ford wheels and they fit too. The hub on a Ford ore Dexstar is a little larger than GM, but that makes no difference because they are stud piloted anyway.

http://www.etrailer.com/dept-pg-Tires_and_Wheels-sf-Wheel_Only-sz-8_on_6~1|2_Inch-pc-16_Inch-pm-Dexstar.aspx