Try Kelsey-Hays for new steel wheels, still have them for early Mustangs. If you are looking used try Colorado Mustangs in Aurora Colorado, they have a large most years junk yard. Some times some of the used wheel and tire outfits have wheels but you need to know what you want, 5 on 4 1/2 bolt patterns are fairly common and if you want stock the 14 x 5 is the standard size and the rear offset is about 3 inches. Another source is swap meets. Since I don't know you, this may be redundant info, good hunting. One last shot is Bart Park (Phoenix), he has piles of used early Mustang parts, you can contact him at 602 843-0041, if he doesn't have them he may know someone who does.