We have had at least two students come to the desk looking for marketing campaigns for beverages that came out in the 1960s and 70s. There are a number of things that might be of help, including:
Advertising Slogans of America (reference HF6135 .S53 1984 )
Every Bite a Delight and Other Slogans (reference HF 6135 .U73 1992)
International Directory of Company Histories (Reference HD2721.I54)
Advertising Age may also be of help, though it does not go back to the 60s and 70s in full text. We found a number of articles in the New York Times historical database. You can also search ABI/Inform and Factiva for news sources and trade journals that might have more on these campaigns. Business Company and Resource Center covers corporate histories as well.