www.mustangtuning.com is one place with decent prices. They are replica wheels and you won't get the Stang center cap though. I did see one place on eBay that has the rims with the option to choose the Stang cap, but I don't remember which company it was.
Go with mustangtuning. Its free shipping and there are more than a few people here that are running those wheels. You also get a discount ( Like 5 or 10%) if you're a Stangnet member.