Did you try the door with all your characters, to see if someone already looted the key without realizing it?
Check out the
Save Game Editor topic;
LS Tools looks like (
screenshot) it can teleport your characters. I'm not sure if opening the door triggers anything, though, which may cause problems if you bypass it.
There is also an inventory editor (
MooseEdit) discussed in that topic, but I don't think it can add items yet. I have not tried either program.
