Are you in the USA?
If so its best to get one made to your own specifications. There are a few builders here I believe.
To keep things in line with most peoples superguns, i'd recommend a neo geo spec'd supergun with a CPS2 kick harness. Then get somebody else here to mod you a Sanwa Agetec joystick. Its going to cost quite alot of money though.
This is mine -
Standard DB15 (same as neo geo) control ports. Just plug the game into the harness, joystick in to the supergun and switch on. Well, I have audio connections and video connections obviously.
My Agetec joystick
The idea behind this is of course to have the 6 button setup like street fighter 2. The top 3 buttons provide your tools for 90+% of all Jamma Shmups and the kick harness goes to the bottom 3 buttons. I only have one agetec modded at the moment though. If I want to play 2 player on anything, I just plug a standard neo geo controller into port 2.
The Agetec uses convertor boxes built for me, so it can be used with Dreamcast, Saturn and playstations.
I wanted it neo geo spec for several reasons.
I can use a Neo Geo SCART lead for RGB, I can use the controllers built for the AES system and its all very simple to figure out.
This industry has become 2 dimensional as it transcended into a 3D world.