Greetings!
Actually, I-Core makes a battlegame by the name of Void that includes an army with many human-type female figures, called the VASA. This figure line includes female figs on motorcycles, rather slim and swoopy bikes, not the big, heavy klunkers that Marines use. The line *also* includes a bike with a sidecar sporting a multibarrel cannon. The VDR fun you can have here is substantial (a Gatling Heavy Bolter on a Fast vehicle... ouch.) Bikes would, IMHO, give the Sisters some much needed mobile firepower, a bit tougher than thier universal T of 3, as well...
For Void stuff, I reccomend Brok's Armory:
www.broksarmory.com... they are good folk. Tell 'em I sent you! *heh heh*