There’s a kbin userstyle for PC (do they exist for mobile?) that gives you a sidebar of your subscribed magazines that groups them from different instances! You still have to find them first though.

This is the list of “official” moves, like how r/3dprinting started !3d_printing@forum.rhombik.com and instructed their users to go there. That isn’t to say there aren’t other 3d printing communities around, but that would be a different list like sub.rehab