Where to buy Bridesmaid gowns in New York

Hi There

I live in Scotland and my sister lives near San Francisco and we plan to meet in New York on the weekend on 26th April to look for her bridesmaid dress for my wedding on August 18th (2012)here in Scotland.

Help ladies I don't know where to start looking for vendors and am I too late to make appointments.

Any help will be very grateful.

Mcmairi