I'm not sure what you mean by having two people look for you. One boutique SA should be able to search all Chanel boutiques, so maybe you have a boutique SA and a dept store SA (e.g. Saks) looking for you.
If you are not using a Chanel boutique SA, try Bellagio... I've always had good luck there with finding hard to find shoes and the SA will look at the computer. I love the slingbacks and have several pairs. They literally go with everything, from work outfits to skinny jeans.
Another option which I am now beginning to do is call Chanel customer service. Let them know the shoe and your size, and they will actually tell you what stores have it in stock. I then had the option for the store to call me or me to call the store directly. It has worked great for me, and I've used this process three times (once on white with black cap toe slingbacks that were nearly impossible to find).
Good luck to you!