Resources for finding all drugs of a certain class
The WHO has their own methodology, the Anatomical Therapeutic Chemical (ATC, thank you commenter) classification system, for organizing such data (its impetus is comparing results between studies).

Also, if you have $900 sitting around, you can get a subscription for the United States Pharmacopeia.  I'm not sure if that can be spread across multiple subscriptions for an organization like the Red Book David mentions.