About a week ago I sounded the alarm, pointing out some of the signs of the Availability Problem of Books on Amazon. Some dismiss it as non-existent, some think it's a kink easily fixed, and others--me included--see it as a serious problem: a problem here to stay, one we authors must contend with.
Since then I found an interesting article. It describes the problem with a focus on the relationship between Amazon and Lightning Source, the leading provider of POD books, and offers an interesting solution. You can easily replace 'Lightning Source' with your own provider, and you can see that the outline of the problem remains the same--except of course CreateSpace, Amazon's own provider.
The solution proposed in this article is interesting, but requires some work on your part. The basic idea is to take advantage of the way Amazon supports books published by its own CreateSpace, while 'guiding' it, by means of price competition, to match the price of your book to its offering by your POD provider, so the profitability remains the same.
Check it out: In Pursuit of Plan B by Aaron Shepard.