Build your own. If you don't know how to build the RGB converter, then just order the circuit from
www.jrok.com
It's pretty damn simple to wire the joysticks, you order the parts from
www.arcadeparts.com and go to an electronic store to pick up the wire and the connectors.
It's not all that hard, and as far as super guns looking ugly, I know it's pretty ugly with the PCB hanging on the outside, that's why I'm designing mine to have the PCB inside. Also if all goes as panned, the wood will be finished, as well as have cool Neo Geo/SNK decals.
Peace
JHendrix