Your mentors need not be only women. There are many more men in senior faculty positions than women, so statistically, it will be easier to identify male mentors. Female mentors may be relatively scarce and at times, non-existent. If they do exist, they tend to be very popular and already to have many mentees. Mentors of both genders have much to offer. While a male mentor may not be able to guide you as much in work-life balance issues as a female mentor with children, he may offer you valuable insights into the politics of academic medicine. That is exactly why you need lots of mentors, both men and women.