I had the same problem last week - in the past, either my BA locator has worked, or I have been able to find the AA locator using CMT. Last week both failed for me, but I managed to access the seat selector on AA by 1) registering for an Aadvantage account, and logging in, then 2) searching for my booking by date / flight number / name, and then it worked.

I think you need to be logged in as Aadvantage member to be able to access the necessary search page.

Hope that works for you too...