Just want to add something really important.
If you have the Gold Edition, you CANNOT get this. Since Episode 8 is on the disc (and what seems to be causing many of the DLC related achievements problems) and cannot be removed, you won't be able to get it. You can get ALL 31 original costumes... and nothing happens.
However, if you have a save from a gold edition, OR got all the costumes unlocked on a gold save (as I did), you CAN play that save from a regular edition. Just get one of those, accept the update (you don't have to refuse it as people say), ignore the 'free DLC' message, and just go on as you were.
OR if you had all 31 before, just replay any level and you'll get it upon completition.