I think I had to mail order mine, but it wasn't fan made (unless the fans worked for General Mills).
Back in the late 1980's / early 1990's there were kiosks in shopping malls where you could go in and have your picture superimposed on the cover of People Magazine, The New York Times, Wheaties boxes, etc. They would either take your picture or you could bring them a picture. This is back in the pre-Photoshop days where you couldn't just to it at home. There also may have been a promotion from General Mills where if you sent them your photo and some amount of money they would would do the same. My understanding is that these boxes originated one of those two ways, and were not a product you could buy on store shelves.
Lee