Try the public schools archives. Sometimes families donate yearbooks or/and schools donate them also. All books may not be there but it is a start. Have you checked with the school in question. In my state, I requested copies of records for my father and was told about so much more. It was the first time I saw him as a young boy ever.
Sometimes other religious schools have archives also. You just have to go there and ask. A face to face can get you further than a phone call. I always take proof of what I want it for. There are identity thieves out there. Ex. Take your proof of ID.,drivers license, passport.