What about Matcatz wireless brawl pad, as it operates differently then the PS3 controller, and doesn't actaully sync to the system, it is totally independent of it once you unplug the USB wireless connection thingy.
Side note, this is why I have no idea why PS3 is the standard system for MK. at least with Xbox you can by wired controllers made by the company that makes the system.
Side,Side note. I bought the wired PDP afterGlow controller for PS3 to see if it was anygood, as it's one of the only wired PS3 controllers out there, It sucks ass, stay away from it.
Having to buy a converter and an old controller is just dumb.