[ARC5] U.K. TR9D: Ray R. Does the Impossible!

[David Stinson]

Ray Robinson, our great member from Australia, 
has done the impossible:  found the parts I was
missing for my "Battle of Britain" TR9D rig!
I am in your debt, sir.
For those of you suffering under the unfortunate 
and common delusion that The Battle of Britain 
was fought with VHF radios in the Spitfires 
and Hurricanes, be enlightened:

"...the TR 1143 was not forthcoming in time 
and the Battle of Britain was fought largely on HF 
with the old crystal controlled TR9 with which
I was still battling as late as 1943! 
By September 1940 only 16 
day fighter squadrons had VHF. "
      Doug Tidy HF/DF Operator 74 Squadron "

"In August 1940, HQ Fighter Command decided 
to restart the changeover to VHF R/T...
However, by the end of September 1940, 
the TR.1133 installation programme 
was not sufficiently advanced for Fighter Command 
to take full advantage of the 'superiority of VHF over HF R/T'."
     RAF Signals Museum, Bedfordshire

Anyways- The TR9D uses these U.K. valve types
  (note: "VT"/"VR" in this context has not relation to 
    U.S.A. Signal Corps "VT" or "VR"-types):
VT50
VT51
VR18
VR21
VR22
VR27

How difficult has it become to find these valves in good condition,
and how expensive have they become?
Can "dead" examples be found, so I can experiment with 
tube substitutions using the bases?

Thanks,
Dave AB5S