I use these guys:
http://www.inmoba.com/about/online-r...-crm-software/ - they are in Spain though, but it shouldn't matter if you just want it for tracking purposes.
Commissions on €10m villas are rather tasty
Personally, I'd find out who the top real estate agents are in Manhattan, and set up a deal with one of them - % sales commission basis, or paid per lead. It's around $1 a click for adwords for the better phrases in Spain, so that should give you a bit of a guide.