I use ITN, expedia, Travelocity, Orbitz, airline sites to look up best fares in a particular class. However, I am not sure how I can look up the best fares for a specific type of fare.

THis is needed for promotions, etc. For example, some promotions may require B or Y fare type. I can usually find them by calling the airlines but I would like to research on the Internet first.

Is the only way through a travel agent or a professional subscription to Sabre?