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Here are some ideas:

lobste.rs has a invite system where a person who invites someone may potentially be kicked if the person they invite is a problem. See https://lobste.rs/about#invitations

Organize a booth or representative at women-focused tech events like FFC or GHC, or have events/meetups for Leap members to meet face-to-face where prospective members are also invited. The invite system would make this easier to implement.