Try
www.itn.com. It belongs to Amercian Express, but u can create your own login, and don't have to be a cardholder. Go into "My Account" (top LHS) Select "Display Preferences" and change it to "an expert".
Then this will show all the flights avail. between the selected City Pairs, return or one way, with the avail. in ea. class, eg F J D Y etc, so u can see how the plane is looking in terms of availablility. It is a very useful thing for staff travel, but isn't completely accurate, nothing ever is.
They have changed the site recently, so experiment and see how the new software works.
Cheers, Enjoy
Kiwi 1