Jules...

You make a very good point. Stores won't carry products that they don't think the public will buy. When more people start requesting a certain product or type of product, stores usually listen.
I sent an e-mail to a large local grocery chain about a year ago complaining about their lack of low carb products (they advertise themselves as "your one stop shopping store" meaning that they have everything you want all in one place). Well...it took a few months, but ever since then I've been seeing more and more low carb products on their shelves and people are buying them.
Whenever I can't find what I'm looking for at my local health food store, I ask and they are usually quite willing to special order it for me if they have a supplier for it.
It also helps to ask other people you know who are low carbing where they find things. One of my co-workers recently gave me a tip on where I could find heavy cream by the half gallon for less than half of what they charge in the local grocery stores. I'm using it to make my own yogurt and also for my DH's coffee and sauces, so I can easily go through half a gallon of heavy cream in a week's time. Buying it by the half pint can get expensive quick!
The moral of the story is....if you can't find what you want, ask for it. If you don't ask, they won't know you want it.