Just curious - has anyone attended the all-women's class at Hombu? How does it differ, or does it?
Back to the original topic, from a promotional standpoint, I guess it would depend on who your target audience within women would be as to how you could market it. If you are looking for college aged women, maybe talking to some of the sororities at local colleges would be a start, or scheduling a demonstration on campus at the beginning of the summer session. If you are looking for the soccer mom demographic, you might talk to the rec department that sponsors the little league teams to see if you could hand out flyers at their events or set up a table. If you're looking for a general 30-50 range, you could contact local yoga studios and bodywork practices (eg massage therapists) to see if they would like to pair up and cross market (ie they hand out your flyers and you hand out theirs). If you are looking for older women, you might want to contact some of the civic and social organizations like the Red Hats to see if their members would be interested. You could also talk to some support groups as well, and target a variety of those. I would think that a cancer survivor group would get as much out of the physical and spiritual aspects of aikido as an abused women's group would get out of the defensive security side.
Just some ideas. However, if you are going to do that much marketing, you might find yourself with enough male interest too that you could consider having two sections, one mixed and one female. Is there such a thing as too many students?