Another slightly roundabout possibility I've discovered is, if you have the ticket #, PNR or credit card number of purchase, go to http://refunds.aa.com , search for the ticket, and click "Select for Refund". On the screen before it actually checks whether a ticket is eligible for refund (and would then go on to let you fill out a refund request), it gives you all sorts of data, including the fare basis code for each leg. Seems to work for all tickets.