There are for sure places people gather. 

The biggest is Station 7. A abandoned, half finished subway station in Queens that a magician turned into a kind of speak easy for magicians. YOu only see or find it if you have modicum of magical talent. 

Another Princess, which is a cafe on Manhattan that is supposedly for mundanes, but Magicians are always there.

As for hidden places and smaller places, there are more then a few yeah.  Magic users don't crowd though. Becouse people have so many different patrons and agendas.