I don’t have an official Mets meetup group or list-serv, but there is a Facebook Group for fans in Chicago to join and talk/plan all things Mets.
I often get emails from people asking if there is a bar in the city that has an affiliation to the Mets. While there isn’t any official bar, I have become friendly with the staff at Finley Dunne’s in Lakeview. They have the MLB Extra Innings package, as many bars in the city do, and are very accommodating putting a Mets game on a TV. Several times, we’ve been able to use their back room and have the game with audio. Another bar that people will get together at is Racine Plumbing.
A highlight of Finley Dunne’s? The pennant they were kind enough to hang for me before they did some renovating: