The first place I tried on a Google search,"Trailer Parts Superstore",has 16.5" GALVANIZED "round hole modular" 6 lug rims with 5.5" bolt circle,and 4-1/4" center hole,6-3/4" wide,for 65.50 each!.(Part # 1350105)...I'm sure if you try searching further you could likely find plain steelies for 50 bucks or less apeice..not too bad a price for brand new rims!..
Don't even think about mounting ANY other size tire on ANY rim!!..if you like having your head attached to your neck that is..I've seen guys blown apart from airing up a 16.5 on 16" rims accidently!..and others who lost control of the truck when it took a 65 mph ride to let the beads give way..