Barnes & Noble does not supply any direct sales data, however it is available from NPD BookScan.
NPD BookScan operates the world’s first continuous retail sales monitoring service for books, with purchase information representing sales through a majority of the major retailers each week. In a typical week, sales for over half a million different titles are collected, coded and analyzed, producing complete market information for retailers, publishers and the media. If you are a publisher or an author, you can reach out to NPD BookScan to find out more about the services they offer and the associated costs.
Use this link to contact NPD: https://www.npd.com/wps/portal/npd/us/industry-expertise/books/