Walmart has the 16.5 Firestones, not too bad a price.
Firestone Transforce HT Tire 9.50R16.5/10
http://www.walmart.com/ip/Firestone-Transforce-HT-Tire-9-50R16-5-10/17790921
16.5's are somewhat obsolete but there are still many sources around.
TIRE RACK...