I do not think researchers get so easy access to Amazon's selling data. I had also tried to have the one while doing my PhD research, but it feels doing so is not a bed of roses. If some one has any idea, that's really appreciable and I would also like to know if it is possible anyway.
I too am interested in Amazon's selling data. I have collected the following data which includes sales from Amazon, Barnes and Nobles, and Book a Million from their Annual Reports for a study I am now doing.