There are a number of notification networks (or "Buff Groups," as you call them) operating in and around New York City:
Citywide Radio New York: 453.000R (167.9)
Metro Fire Radio: 1 - 451.850R (114.8); 3 - 453.000R (114.8) (their East channel)
Citywide One New York: 461.225R (167.9)
New York Central Radio / Metro Notification Service: 451.725R (100.0) and 452.575R (100.0)
Police, Fire, EMS, and Emergency GMRS Radio Club: 462.725R (110.9)
One needs to be a member of the respective organization before transmitting on any of the above channels.
RE: General Mobile Radio Service repeaters in Manhattan. There is a repeater in Manhattan. It is a closed one. By closed I mean that the owner must have a copy of your valid FCC GMRS license on file prior to authorizing you on any of the tones that are active on the machine. In my monitoring experience I find that most authorized users don't use the repeater because they are often close enough to talk to each other on simplex.
Lastly, I have no idea what the Times Square Alliance is using.