Dont know where you are on Long Island, but there are 2 clubs.
The Long Island Bonsai Society is the bigger of the 2. They meet at the Planting Fields Arboretum in Oyster Bay on Monday nights once a month. A member here, NYBonsai12, is a member of that club. Im sure he will chime in and tell you about them.
The Easten Suffolk Bonsai Society is much smaller (15-20 members) and meets every 2nd tuesday each month from March-November in Bellport. I am a member of that club.
ESBS sometimes piggybacks with LIBS for activities and speakers.