He has a lot of published journal articles dealing with specific matters related to his broader research goals, and a few other books that I haven't read yet. Of these, Historical Dynamics seems to be the most relevant to SotE - it deals with a lot of questions related to large-scale human societies, with the same analytical and mathematical rigor as his other work. The bibliography on his Wikipedia page has a list of his most important articles, and you can read brief descriptions of all his published books on his website (http://peterturchin.com/books/). That website also includes a semi-regularly updated blog, which has a big backlog of interesting posts related to his work.
I've become a somewhat active user of the Discord, and I'm sure I'll stick around. I've been following SotE since you left M&T to start on it, but now that I can play around with the 2.0 world generator, it's grabbing my interest more and more.