Yeah, it's a bit crap when the communities you're used to aren't here yet.
My solution was just to create them myself - I've never modded before and tbh, I don't even really want to especially, but as there was no MST3K community yet, I made one, and the same for Arrested Development.
I've publicised them on New Communities, crosslinked them and added a note in each about the mods from the equivalent subreddit, as, if they want to be involved again I'm happy to add them as mods.
Early days, but MST3K has over a hundred subs already, which is not bad when I created a couple of days ago.
Links: