I quite like this approach to bring attention to conferences with poor gender diversity, by Dori Smith of Backup Brain:

Given that I’ve been ranting about this issue for several years now (boy, time flies when you’re having fun, don’t it?) and nothing has changed, I figured I’d try something new this time: creating a group on Upcoming.org called Needs Women Speakers. Feel free to join, and once you’ve joined, you can add “Needs Women Speakers” as a tag to any conference you see where you think it’s applicable.