anecdotally (and not GP), most of the women I am friends with have several good friends in the area where they live and easily make new ones if they ever move to a new place. for many of my male friends, I am the only friend they have in the area.

I don't think I can generalize to entire genders from my experience though. it could simply be that it's easier for introverts to make same-gender friendships, so I only have a set of relatively outgoing women to select friends from.