I wondered when I saw your post if I'd seen one of these by Bobby Sheman. Around 1971, I remember seeing that his latest single was being advertised as a giveaway on cereal boxes that I saw in a supermarket; however, I thought that it was a flexi disc. So I did some searching and found that, while there were some "cereal box" records by Sherman, the theme from his short-lived TV show Getting Together had been made available as a flexi disc in cereal boxes -- and this fits with when I recall seeing this record. Ironically, I had thought at the time that this giveaway was a sign that his recording career was going downhill, and that they were doing this because stations were no longer playing his records -- and the fact that I never heard another new record by him again made me think that I had been right. But from what you posted and from what I found as a result of my searches, I gather that many hit records were promoted in this way as well.

I own a couple by Bobby Sherman, including a Canadian one.