To the OP and anyone else still not familiar with how to get monthly viewing of availability...(obviously you can use BAH's good advice above or other sites...but using BA.com maybe this helps....
One way to check award availability using BA website
You can ignore the first two paragraphs...start at "Then in a browser" bit..
Hope that helps. There are other ways as well to get to the same results and obviously to also book with cash and upgrade with Avios but this may get you started.