One would have thought that Dekatrons were the rarest of tube technologies. But one can still find NOS.
Beam deflection counter tubes, are something else altogether:
http://www.tube-tester.com/sites/nix...rd/e1t-mul.htm

Inventory is essentially non-existent.
Despite of that, some enthusiasts have made some gorgeous projects:

http://www.tube-tester.com/sites/nix...-clock/e1t.htm