A recent book of poems written by a cousin that I purchased on Ebay recently reminded me of a tip that we’ve mentioned before. Go through old books completely page by page to see what might be stuck in between pages. Clippings can be smaller than this one and might not be noticed with a casual, quick, flip through–especially if they are tucked in the spine.
Also don’t forget to turn them over! This one was photographed this way intentionally, but looking at both sides can be helpful and may help you date or locate the clipping as well.