Where do developers and authors hang out?
There’s a IRC channel called #gemini on irc.tilde.chat. The port using TLS encryption is 6697.
Ben has a Delta Chat group. Set it up and send him a message and he’ll add you.
Announcement with contact information (archive.org)
There's an unmoderated newsgroup with some activity:
There was a mailing list (gone since December 31, 2021):