interesting - denial of shipping for NOS vacuum tubes via ebay..

It will be a long, cold day in the nether regions before I purchase a tube from eBay.

That, notwithstanding, there are any number of reputable tube dealers that will:

a) Ship for a lot less than $35 - the GSP minimum.
b) Know what does and does not have mercury in it (83s do, by the way).
c) probably understands that Thorium is also mildly radioactive.
d) Only charge customs fees when necessary.
e) Understand that this is just another eBay racket.
f) Understand the concept of "matched pair" and what it actually means.
g) Backs their merchandise.

I believe that (at least) one of those sorts frequents this venue as well.

Yes Peter - I hope whomever Bob uses for shipping does not put this fence up though.

Another article on this on Hackaday  https://hackaday.com/2018/01/20/vacuum-tubes-shipping-through-ebay-now-challenging/
Some discusions on google groups from the past year https://groups.google.com/forum/#!topic/neonixie-l/o1DLO2amf6g

If this is truly the case we're screwed!

In the google groups discussion the remark near the top is the relevant one I believe
http://wordpress.mrreid.org/2013/08/07/mercury-and-aeroplanes/

"But if the raw elemental aluminium is exposed (e.g. by a scratch) and comes into contact with mercury it forms an amalgam, tearing away at the aluminium and causing it to lose its structural integrity. As the aluminium is eaten away it combines with the air to form aluminium oxide and falls away (as seen in this video). This allows the mercury to reach fresh aluminium and the process then repeats, so a small amount of mercury can do a large amount of damage. If a mercury thermometer were to leak aboard an aeroplane the aeroplane would need to be taken out of service and disassembled to assess the damage the mercury might cause. There have been at least two incidents in which aircraft exposed to mercury have been written off by their insurers."