Hi diamondfairy
I think Bella Findings in LA would do it, but they may only work through local retailers. They are wholesale trade. Their contact info is on this page:
http://www.bellafindings.com/jewelsc..._contactus.asp
If they will work with you directly, you can pick out a clasp on their web page and get the product number, though you won't get the price unless you have wholesale credentials.
###
There is another thread about leaving your pearls to be strung. I will search for it and add it in a few minutes
No self -respecting stringer would switch out pearls, even in the
highly unlikely event they happened to have ones to fool you with. It just doesn't happen in any respectable setting. The pearl restingers jewelers use are proud of their work and their reputations. Few jewelry stores employ full, or even part-time bead stringers on the premises, because they don't get that many orders to restring. Most have to send them out. I think Bella is one of the places they send out to.