Is there any public resource for book sales data?

Ingram, the book distributor, used to have an automated system that would provide their sales figures for a book after you keyed in the book’s ISBN number. I tried calling Ingram today, but received a message saying the number is “no longer assigned” within the company.

I’d be grateful for any other resource that would allow me to track sales for a handful of specific books. I’m looking for a free resource, preferably.