We are just changing where the buttons are. Here's a list of good controllers for the project. This is what I did at first, since I didn't like the way the Sony D-pad feels. The problem is that the PCB in the Sony pad is very, very delicate. There are no nice big patches of solder to connect your wires to, and it's easy to damage the board.
Illustrative photos are available.
I have listed a few suppliers that ought to be able to set you up. I personally dealt with California Games Inc., and was very happy with their service. CGI should be able to mail you whatever you need. You will need about 10. It is probably possible to adapt a PC analog joystick to use with a Playstation.