On the question of where they are, and the cause of their low numbers: I was discussing this at my last gaming session, in which an Objectivist-ish dude and I played War of the Ring (which is awesome, by the way). The following points seemed relevant to the persistent failure of libertarianism to attract female proponents:
1) To start out with, most libertarians are male. Whether this is because men or male brains are innately attracted to libertarian ideas or because libertarian ideas are more commonly found, and thus disseminated, in male-dominated social groups or tribes (SF fans, CS types, high school nerd clusters, etc.) is a separate question.
2) In opposition to traditional statist positions regarding the need for coercive intervention to prevent discrimination against women by governmental entities, corporations, and individuals, male libertarians often go so far as to deride the general goal of social norms of gender equality.
3) Women see this and recoil. The male domination of libertarianism continues.
If libertarianism is about free human flourishing, then why wouldn't you, a libertarian male, push civil society to allow for the self-actualization of half the population? Wouldn't you be concerned about the extent to which female* children are inescapably victim to the coercive inculcation of beliefs about gender that are destructive to their full personhood? Wouldn't you want to admit, for the sake of your female listeners, that even if you disagree with government intervention to remedy sex discrimination, you still think sexism is wrong? (If you want to say people have a right to be bigoted, it's prudent to condemn bigotry; cf. Rand Paul.) If libertarianism is to attract women and be viewed as more than "f*** you, I got mine," then a little empathy would go a long way.
* And male [PHMT genuflection].
UPDATE: Phoebe gets at what I was going for. If a libertarian man's default stance is to scorn attempts to control behavior and conventional wisdom, then you're going to throw out some feminist baby out with the bathwater. Oddly, IIRC this sort of juvenile oppositional posturing is one reason why Ayn Rand thought libertarians were not potential allies.