You can check on the AA site a little more easily, even though it is with booked via BA. Look for MileSAAver availability, that should also be available on BA - and online at that. I seem to recall AA have a slightly shorter window for availability than applies for BA, so it may be worth waiting a few days to see it that will improve matters. Also check the cash fare for buying, it's relatively inexpensive on that route and you may be able to use your Avios in more fruitful ways.