Hi. I'm new to the Mudcat, but I might be able to offer a little help.There are great Irish sesiuins in NYC--populated by nice people who *might* let you join in.
Try Swifts on 4th & Lafayette Tuesday nights at 9:30 or Paddy Reilly's on Thursdays at around 10
There are also sesiuins at Mona's, Kate Kearney's, the 11th street bar (11th & B)
Good luck & enjoy your trip to the city!