I don't know if you're following my new Twitter feed, @aisledash, but tonight I attended a preview of four Oscar de la Renta dresses exclusively at Bergdorf Goodman in New York.
It's rare, but some designers do make wedding dresses specifically for a salon. The salons selected are usually high-trafficed/high-sales businesses like Bergdorf and Kleinfeld. When you're trying on wedding dresses at any salon and the salesperson says it's an exclusive to them then you won't find that dress anywhere else. Don't think the salesperson is lying just to make a sale. If you do think it's a sales tactic you can always call the designer's office and ask if they have any exclusives with the salon you visited.
While exclusive dresses are one-of-a-kind wedding dresses, more often than not they are variations of wedding dresses already on the designer's line. So if you do like an exclusive dress but think it's a littl e out of your price range ask to see the rest of the designer's collection because a less expensive version may be available.