Being a parent in NY as an MBA is very different from Asia. No maids! As a start on where to look I recommend the Parent's League. They give very good information on schools and babysitting services.
Parents League: http://www.parentsleague.org/
Be warned schools in the US close a lot! They close for snow, they have holidays that people working or in university don't have. Besides a school you will need a babysitting resource and a backup babysitting service (which can be more expensive) for night dates and things like that. The second service can be one of the services that tourists use which background check the sitter for you. These don't always send the same person though.
Gocitykids on babysitting: http://gocitykids.parentsconnect.com/browse/subcat.jsp?area=197&category=840
