CUSTOM! Honestly, if the stick is for a CMVS only, making a custom Joystick is the easiest damn thing ever. You essentially can't screw it up, and if you do, the worst that happens is a button doesn't do what you thought it would, in which case you just swap wires until you get it right.
You need to buy:
1x Joystick. I love Sanwa, but you can get a Happ/Seimitsu or any brand you want.
6x buttons. Get them in any color size and shape or brand, I bought Sanwa OBSF30's
1x DB-15 serial port.
12x Crimp on quick disconnects for wires
Some wire, easier if you have a ton of colors, but not required. MAKE SURE to have one that stands out from the rest for your ground wire.
5x Crimp connectors if you got a Sanwa stick, you can't use quick disconnects with them.
An enclosure, It can literally be anything big enough to be a joystick. I used Hammond Mfg #1456PH1WHCWW
https://www.hammfg.com/electronics/small-case/general-purpose/1456cww
30mm Hole Saw
15pin serial extension cable JNX sells them I think, you can find them on ebay and amazon too
www.focusattack.com sells all the parts you might need except maybe DB-15 port which you can get from digikey.com.
You'll need to know how to wire up an arcade stick (plenty of guides out there, it's really easy) and if you feel so inclined, decorate it a bit.
These are mine, I essentially did what I just described, I'm an electronics noob.
Technically mine are also USB for use on PS3 and Windows/RasberryPi hence the additional 4 grey buttons (they aren't hooked up for NeoGeo), but that hardly made it more complicated. If it for NeoGeo only it's about the easiest project ever with awesome results.