That picture of the Majorca necklace is very helpful. If that is the strand you like, but in real pearls, you could have one made exactly like that--but in freshwater baroques that look very similar to those. I don't have the name off-hand of anyone in the U.S. but that should be easy to do. The Majorca ones are 12mm. Have you considerd the size you want? You can figure the exact length you may want by just using ribbon or string to measure how you want it to look. (I think the measurement on the Chanel necklace was probably wrong--even a thin neck is usually aroung 11-12"--and if there is no clasp, it is always difficult to get the last strand over your head if there isn't enough extra room).
I think QVC and Ross-Simons both have nice longer strands, and you may be able to find some in local stores. But if you want a custom specific length, specific size, pearl necklace (perhaps, with a specific clasp too) then you can probably find that locally or via the internet with a custom order. If you live near a "China Town" (since a lot of the fw pearls come from China) or near a beading shop, someone there may be able to recommend someone locally.