Sometimes people pick other names... maybe search for people talking about housing issues. Not 100% correlated with YIMBY, but people thinking about similar problems: https://www.strongtowns.org/local

Or start something yourself! Where do you live?

If you know of initiatives you care about (like SB 50 for example), look for groups pushing that.

If you're on twitter, the twitter networks usually bridge cities. I follow a lot of LA area YIMBY groups, but get some cross pollination from other cities too.