mlawless: Hello and welcome to FT! I haven't found a system that will let you search by fare codes since the good old easySABRE days. It's too bad it is no longer available. Maybe they noticed that revenue per pax was lower than other ticket sales channels.

Anyway, on ITN you can see the availability for each fare code. First you have to sign-up as a member. Then sign-in and modify your Travel Profile. You need to change the Availability Format (under Display Preferences) to "an expert." After that, when you search for available flights (using the advanced search option) each flight will show the availability for each flight by fare code.

Good luck!