I have a friend who is into hackathons, and have been going to a few lately, but it's hard to find a good comprehensive list. I build the list for this site by scraping from a bunch of different APIs (eventbrite, meetup, etc...) and a couple of websites (devpost, MLH.io) to create potential listings. Then I manually curate, review, and post them. Hopefully someone else will also find this helpful, even though it's only focused on SF and the bay area for now.