"banned books" has a number of connotations. In common PR culture it refers to books that school districts have censored, but are otherwise generally available for sale .

In this article they are referring to popular books on Amazon that are censored from theocratic or Islamist countries.

If you want to find the real banned books, look for books that are $300+ on Ebay. Those are books that publishers refuse to publish and retailers refuse to sell. I'm not aware of statute banning those books, but they are in a practical sense banned from publication.