The So Reals are Ebay from time to time for $30-$50. Scenes Unlimited has rubber casts that are nicer than the originals. They also have some rims, but from what you are describing, they are probably not what you are looking for either. If you are skilled with the lathe, that is probably your best bet. I too, have a hard time finding rims for 4x4s in the styles that I want. Your other choice would probably look better if you could pull it off. Since the tires are resin, you may could make a plastic insert, then sand it and mold it into the rest of the tire to get it closer a 15" instead of an 18". That is something that I have always wanted to try, but have not been brave enough to tackle it.