spare tire

I'm needing a spare tire and wheel assembly for 68 dart. The car has been converted to the large bolt pattern. Anyone have an idea on a wheel I can purchase that will have the correct offset so the spare tire hold down will work? I would prefer a 15 inch wheel and have been thinking about purchasing a rally wheel from Summitt.
I'd love to have one of those polished aluminum wheels out of a big ford or merc but can't find one around here.