I wanted to try a mixbox but didn't want to build a whole new stick so I modeled this adapter design. It mounts in the same holes as a standard sanwa joystick and the key switch wires go through the stick hole. Prints with no supports in 2-3 hours.
You'll need 4 m4 nuts and 4 m4 machine screws in whatever length will go all the way through your panel and the adapter. You'll also need 4 mechanical keyboard switches of your choice, I used gateron blues because that's what I had laying around. For the wiring it's whatever. I soldered some solid 22 gauge copper wire to my switches then poked the other ends through the quick disconnect wires for my zero delay encoder and twisted them on so I could reuse everything after.
No supports needed if you print it on it's side. I printed with 40% infill which was probably overkill so lower it to 10-20 to save some time and material.