Yep, the Mil have a separate frequency for P Pans/Training Fixes, or did when I was a Mil ATCO. And, yes, a separate freq in the VHF band COULD be made available I am sure. Now the cruncher!
WHO's GONNA PAY FOR IT!
Have you any idea how much it would cost to have all the separate 121.5 relay stations equipped with an addition Tx'er Rx'er, forward relays, landlines etc not to mention the integration of this kit into the D & D cell?
As it was, the civilian community would only go for autotriangulation on 121.5 in the SE of the UK because the last update was "too expensive" to encompass the whole of the UK! Hard luck if you MAYDAY on VHF below 8,500' in Scotland as the relays are few and far between and rely on manual plotting of bearings - yes scrabbling about on the floor with maps, rulers and pencils IS the order of the day.