I've taken it upon myself to find Buttonhead a singer...
They are brilliant. I know for a fact they've label interest, all that jazz etc. They're even playing the LastFM Xmas party. So yeah.
You need a "natural mid-to-high range", apparently. And to be in LDN. Being reasonably young wouldn't go amiss either.
Listen here http://www.myspace.com/buttonhead
My work here is done...