If you have a specific interest/activity such as gothic cathedral architecture, hiking, scuba diving or romantic castle tours, try searching in those areas which would most likely have resources for female only/majority/focused tours.
I've been on a few golf, foodie and of course shopping tours organized by various universities, women's clubs and charity organizations. Sometimes even private clubs will allow you to join their tour as a tag-a-long if they need to make a minimum or reach a head-count for a certain discount, so it's ok to leave your contact info even if the receptionist/doorman says that their trips are for club members only. I've been called by the organizer this way before and invited to join their trip.
