Once a book has been published it will need a distributor.
If your book has been published by an established publishing house they will already have distribution contacts. If you self-publish or publish with a very small house that does not have distribution set up, you will need to make this contact on your own. Remember that distributors will generally take 55-65% of the cover price (40% of which is going to the bookseller). Make sure your pricing formula has taken this into account.
#8 - 19272 96th Avenue
Sandhill Book Marketing Ltd.
University of British Columbia Press
Firefly Books Ltd.
Fitzhenry & Whiteside Limited
(800) 646-2879 (Toll-free orders)
The ACP's Higher Education committee has addressed the issue of stocking of primarily used copies of textbooks in an open letter to campus bookstores.
Read the letter here.