What system are you planning on using the wireless device on? (And does it have the analog joystick or is it just the control pad with 6 buttons (Much like the sega Megadrive pad). If It is the PC (Which I presume it to be) then you should be able to hack some kind of wireless pads PCB into the existing, If it is for the saturn then you are going to be :---steaming pile of meadow muffin---: outta luck There are plenty of wireless gamepads, the hardest bit would be making the pcb from another device fit neatly.
I think the question should be, does anyone know of a wireless gamepad with easy to solder points. (Those sixaxis ones look incredibly small to me).