For the series 56, you will need to find a CBSX-registered broker-dealer. There are quite a few firms you can likely get a series 56 with in NYC. Here a few to start (some may not be CBSX firms but rather FINRA firms. Pardon me if I make an error):
Avatar Securities
WTS Proprietary Trading
T3 Trading
Hold Brothers
Legend Securities
Wall Street Trading
LES Trading
SMB Capital
Chimera Securities