Yo guys!
Just wanted to give an update on this situation. I ended up buying a switchbox from Mitch and a power supply from eBay, and both of them worked great! After some searching, I got a controller for $25 from a local second hand appliance store (go figure). The controller was broken (obviously), so I opened it up. Somehow, the circuit board had gotten wrinkled under one of the side fire buttons, so luckily the previous owner gave up on the the controller fairly quickly, because this rendered all of the top buttons (along with one of the fire buttons) totally useless. So after I realigned the circuit board, all of the buttons worked perfectly!
But, the problem is, when I put the Joystick back on, I can't get the lower nub on the bottom portion of the controller to align with the nub on the top portion of the controller. This results in me not being able to move the joystick down, and when I force it down, it ruins the calibration of the lower nub and makes the joystick unuseable. Does anyone have any tips for getting them to align? I've opened and closed the controller about 10 times, trying to center the joystick as much as possible, but I just can't get it to align.
Also, the circuit board on my controller is white, and not green. Does this mean it's rare?
And thanks for the extra information, Sdamon. I was about to go for just a third party controller, but held off once I knew you needed a real 5200 controller. And thanks Shadow, once I have it up and running I'll definitely be on the lookout for those games!