Alibris.com is a used book seller with a lot of available books for sale. 

Google Products is another search engine in the Google family.

This link will load a list of all USAF yearbooks currently for sale on Ebay.  This is not a static list, it is custom code using the ebay API , so every time the link is clicked, it searches the Ebay database to produce the list (so it could be different from minute to minute).  Will open in a new window.

EYearbook.com is a subscription website so it should be used as a last resort.