Once (or twice) a year, Scott Alexander does a big push to organize ACX meetups all around the world. When I've done interviews with many existing EA, Rationality and ACX groups, this is often the time they got off the ground, as it is for many groups the first time they reach critical mass. All you have to do is set a time and place, and show up to meet other people who also like reading Scott's blog.
You can volunteer to host a meetup in your city by filling out this form. The deadline is the end of the day on Tuesday (two days from now).
If you want more details, check out the ACX post announcing the meetups, or ask me questions here.