We seem to have a similar problem at our club, since March 2007 we've had one solo female (Flossie), one female duo (Ember) and two bands containing women (Isambarde and Anthony John Clarke with friends), the rest have been all male acts.
We're having a girl's night next guest night which is a culmination of the ladies we have as our guest night support acts, a duo and three soloists, the amusing part is that one of the soloists is me!!
We had another duo come to our last singers night but we seem to be a club that is short on female performers, I'm not sure I can come to a reason for why!!