It's no special connector, pretty sure they're just any old banana plugs you could get from any electronics or hifi store. The better quality ones are gold plated and a tighter fit and can no doubt have less resistance (this is a good thing - go for expensive gold ones).
If you want to buy something already made up I'm pretty certain
http://www3.towerhobbies.com/cgi-bin...&I=LXNCU4&P=ML will fit. FWIW 12ga is probably overkill for charging, I have the hyperion 0610i duo (12s 360W) and they recommend 14ga wires less than 200mm long.