Genealogists and local historical researchers often find previously owned school yearbooks valuable, because yearbook signatures from classmates can offer interesting insights into a community's history. Additionally, some people may have lost their yearbooks and just want another copy. Fortunately, researchers and alumni can usually track down a specific yearbook.
Online
Online auction sites like eBay as well as sites specifically dedicated to procuring and reselling yearbooks may have the yearbook you are looking for. Online sites offer both originals and scanned digital versions of old yearbooks.
Schools and Libraries
Some schools purchase extra copies of yearbooks and may have extras available. Additionally, many schools now offer digital versions of yearbooks, drastically lowering the price. Many libraries also digitize their archives and may have electronic versions of yearbooks in their collections.
Publishers
Book publishers often archive anything they publish and may be willing to reprint and sell copies of old yearbooks, though it may be expensive. A few publishers, such as Jostens, Herf Jones and Taylor, handle a large volume of yearbook production in the United States, and the individual schools or district offices may have a record of the publisher used in a particular year.