Here's the RUNBA karaoke, with the female backing track. My audio-fu is weak, so there are a few screw-ups here and there. For example, the male voice is there for some ensemble parts ("odoro yo boku-tachi wa RUNBA", the first wakaranakute) and some of the female backing track is removed because it overlapped to much with the lead's voice to be recoverable.
On request, I'll completely remove all parts where the male voice is audible (at the expense of the girls' voices), but I can't recover the 'shinjite runba' part towards the end.
Didn't a Karaoke version come with the single?
Without the girls voices, yes.