Yes, Victor has a special stash, which alledgedly are the best of the best, but will set you back $300/tube, if you act quickly. That price has gone up three fold in the last 5 years, so they won't be getting any cheaper as the supply dwindles.
Also, Adam, the VK-52SE uses (8) 6H30 tubes, not (6), so it would cost $2400 to re-tube the VK-52SE with Victor's special stash.
Cheers,
John