You might want to contact the people involved with Golden Age TV Recreations
http://www.golden-agetv.co.uk/ and Museum of the Broadcast Television Camera
http://www.tvcameramuseum.org/ I am sure they would have a figure on what exists of British cameras.
I personally have been lately considering doing a survey of what old cameras exist here in Australia, both British and American and making website in regards of our old cameras as I've lately become so fascinated with them. I personally want to find out if any RCA TK-31s used by QTQ-9 Brisbane and NBN Newcastle still exist today in the hands of museums or collectors of the stations themselves.