One of the problems with such rarities is that they do create speculation!
I have a dim recollection that the eBay sale Peter mentioned fell through?
At about the same time there was also a story came to light of an Emitron being found during the clear-out of television centre.
So far as the history is concerned, I did study this formally and Chapter 5 of my thesis describes the rivalry and co-operation between the inter-linked transatlantic Marconi, EMI and RCA companies. It's available on line at:
https://www.research.manchester.ac.u.../FULL_TEXT.PDF
A definitive list of Emitron camera tube survivors is probably never going to be possible, but even rarer are the Baird Television Limited's versions of the iconoscpe. The only known survivor of those is at Strathclyde University, but are there others?
These mid to late 1930s tubes are rarer than Rembrandts, but sadly they're not treated with anything like the same reverence!
Best regards,
Paul M