High school yearbooks are usually the property of the school and not the publishing company who printed them. The high school may have an old copy of the yearbook in question or may give permission to reproduce a backdated copy directly from the publishing company.
In the event that the high school no longer has a copy of the yearbook in question or the publishing company cannot reproduce the yearbook needed, there are several other steps to try. Contact the local library in the high school neighborhood and see if the yearbook has been archived. Connect with old high school classmates online and offline to see if the yearbook is sitting around unused in someone's garage or basement. To reach a wider high school audience, start a group or send a message on social websites such as Facebook or Twitter to locate the yearbook.
Put an advertisement online via a website such as Craigslist, and look through the memorabilia section of eBay to help with the search. Going through these searches once may not be enough to find the yearbook, because new listings for yearbooks are added at different times. The search process may take some time, with consistent and diligent follow-up.