I see a lot of searches and a lot of people posting questions about how to unlock the alternate costumes in Street Fighter 4 and Super Street Fighter 4. Unfortunately this is one of the few things that you can not simply unlock in either game, these have to be purchased through the DLC programs on Xbox Live and PS3.
On a good note though, if you purchased the alternate costumes for Street Fighter 4, they will work in Super Street Fighter 4 (they do on the 360 anyway, I haven’t verified this yet on the PS3 but I would imagine that they should).
Apparently they are releasing new “Super” packs for Super Street Fighter 4 though over time, and should all be available by the end of July 2010.