Jumping into 1977, Mike Schecter and Associates made round cards (discs) in 1977 and 78 mainly, most with advertising on the back for many types of businesses. Most are fairly easy to find thanks to Ebay, some are tougher. I'll go through all the discs alphabetically, with anecdotal evidence on which ones I thought were the hardest to find.
Here is the Big T - Tastee Freeze disc from 1978.
Enjoy a little song about a Tastee Freeze while looking at this thread
http://www.youtube.com/watch?v=-uq-Pf13HQo