While Lufthansa does release first class award space to partner airlines within two weeks of departure, the exception is US Airways, since they block all Lufthansa first class award space. I guess with the number of US Airways Dividend Miles bookings in Lufthansa first class in the past, it was costing US Airways way too much money, and as a result they’ve entirely blocked Lufthansa first class on all routes. Now, you can try to get an agent to manually request the seats which in theory should make them available, though US Airways agents have specifically been told not to do this, so it can take some serious persistence.