How do you find information on old commemorative medallions?

You could start by searching the Coins section at Ebay and the other related links below, which are Exonumia, the Token and Medal Society, and the Coin Club. == == Commemorative Coins can be found in the current US Coins Red Book by R. S. Yeoman. For Commemorative Medallions, you would need to look at a book about tokens and medals. There is a group called the Orders And Medals Society of America. This is a group of collectors that collects medallions and are a wealth of knowledge and they may be able to help you. They also go by the acronym OMSA. (see related link below)