Yep, mazdaformance.com, mazdastuff.com, ebay, and used from someone in here.
You just have to keep your eye out for people selling their MP3 rims, do a search and then just start PMing people asking (that way you won't be posting it on a thread where a bunch of people can just jump at it when you're looking the other way).
edit:mazdastuff has them for $256 each