At the main menu, using the D-Pad, press the following directions to unlock alternate attires.

Effect	Code
Austin & Punk Attires	Down, Left, Up, Right, Right, Up, Left, Down.
Roberts & Orton Attires	Up, Down, Left, Right, Up, Up, Down, Down.
Savage & Morrison Attires	Left, Left, Right, Right, Up, Down, Up, Down.