Ironmongery direct is a good place to start for such things. Have you considered getting a panic bar fitted? There are ones available for twin leaf door sets.
It opens inward, so a panic bar wouldn't be much use I think! We're also looking at escape ladders for the other end of the flat - just trying to find somewhere strong enough to mount some Petzl Coeur bolts or similar.
Also for @Aroogah upthread
Ironmongery direct is a good place to start for such things. Have you considered getting a panic bar fitted? There are ones available for twin leaf door sets.