I know you are in the downtown area so I would suggest Bellas. They have a lot of findings and beads - nearly every style you can imagine. They also have a large selection of freshwater pearls for designers. There is another beading store next to them as well, but I do not recall the name.
Bella Findings is located at:
607 S. Hill St., #6
David is the owner and a very nice guy. If he is not available speak with Dana. She has the best knowledge of the available stock of beads and pearls I think.
By the way, they also do stringing there for a pretty good price. But you have to buy something there for them to do it. But that can be something as simple as a clasp.