One might argue that LessWrong is such a thing. :-)

Since we seem to be in more or less the same place, would you like to orchestrate some kind of coordinated study schedule? We could very easily use this site's private messages to have a brief conversation at a prescheduled time every week- hold one another to study schedules, discuss challenging exercises.

Less Wrong Study Hall is also still a reality I think, although not one I've tried personally.