I have seen some repair technicians solder ribbon connectors back together but it usually makes them much more rigid to the point where they won't bend much after that. You are likely going to be unable to fix that. Spare parts?!?! Not likely available anywhere since these are cheap wired controllers.

If it isn't detected by the switch, then you likely have a severed ribbon cable (shown in Step 4) or a faulty MM32L052NT (shown in Step 9). This isn't a complicated product, but you'd never be able to replace the MM32L052NT and reprogram it (you lack the source code).

Doubtful that you'd be able to find a replacement unless you have another set of the same controllers. The ribbon cable is supposed to come out of the latched cable connector like shown in Step 3. You should be able to put it back into the cable connector and flip the latch back down to hold it in. The cable connector is very flat and the ribbon cable only fits in from the one direction. Hope that helps.

Ryan, I have previously commented on another post that the joystick looks like an exact match for the Xbox 360 controller joystick. I would suggest you give it a try.

In Step 8 picture 1, you see the light-blue connector to the button board with the assign/turbo buttons. I would carefully inspect the rubber buttons, the boards, the connectors on both boards, and all of the traces on the boards around that area to make sure that nothing was damaged during your successful joystick replacement. It could be something simple like a knocked of component, damaged trace, cracked/cold solder on one of the connectors, or a number of other possibilities. Your best bet is to find the traces that go to the assign button and trace them back to the processor chip. Try doing some continuity tests using an electronic multi meter.

The joystick is soldered to boards inside the controllers using thru-hole leads. You would want to de/un-solder the existing joystick using a de-soldering gun or soldering iron with a solder sucker or desoldering wick/braid. There are various techniques for de/un-soldering large thru-hole components. All are painful processes. Please do your research.

Sorry, but I didn't get the joystick model number or anything when I tore it down. I hope someone else can help you out. However, if you look at the back of the board, the layout of the pins is similar to older xbox controller joysticks.

Lay the two halves next to each other, lift the locking bar on the board-side connector, use tweezers to hold the cable (like in pic 3 of Step 3), insert the end of the cable into into the board-side connecter (make sure to insert it all of the way), then lower the locking bar.

Which part? The ribbon cable, the connector, the spudger, or the entire Left controller?

I doubt you can buy parts for these. You would have to salvage from another controller or attempt to repair the cable with micro-soldering.