I don't believe there would be any 3rd party controllers that will work with DJI drones. Since the frequency used is proprietary to DJI. It would be nice to just use your cell phone for short distance flying as some drone manufacturer's do. Would be great for a follow me mode.
It's not clear from your question whether you are you looking for a different kind of controller or just for any controller that works with the MM2.
If you just want a controller, go to ebay and find someone who lost their MM2 and is selling the controller.
I have a feeling that one or two other recent DJI drones might use the same controller, but they don't show the model number in the specs, so I can't check.
If you want some kind of 3rd party controller, that won't be compatible.