Used books tend not to sold alongside new books in a bookstore.
However there are a great many second hand bookstores in most towns
including charity shops. Alternatively books may easily be
purchased online from Amazon Marketplace, eBay or Abebooks.
The books are sold @ Borders, Barnes & Noble, or basically
any bookstore w/ a teen section. Or you could order them off of
Amazon or some other Internet website where you buy books and other