We have had good luck scoring F mileage tickets on both BA and AF. The partner desk is fantastic, but they can only search so much, so I do a preliminary search on routes and availability via expertflyer.com. We look for 5 tix at a time, so usually start about 330 days in advance. Some partner desk people are more patient than others, so if you don't have luck with the first one just call back a few days later.