I have a cheap VogaTek SuperGun Mark III if you’re interested. RGB SCART output, but it is a screw terminal for the controls. It’s made with the Neo Geo in mind so the terminals are for 2 players with 4 buttons each. You can still do 6 buttons each if you wire buttons 1-3 from your arcade stick to the Supergun and wire buttons 4-6 to your kick harness of choice.
It’s cheap ($40 shipped). It’s just the barebones Supergun. You can Google it. I will be headed out of town in the morning and won’t be home until Thursday night. I can still answer any questions but I wouldn’t be able to get pictures or ship it out until Friday.