The primary texts of SA are Sexaholics Anonymous (also called the White Book) and also the original texts of AA: Alcoholics Anonymous (commonly called the Big Book), and Twelve Steps and Twelve Traditions. Meetings also read from other SA and AA texts (like Step Into Action).
You can buy the White Book by following this link.
Other SA publications can be purchased here.
AA publications, like the Big Book and Twelve Steps and Twelve Traditions can be found here.