There have been occasional threads about photomultipliers in the forum. The main UK manufacturer used to be Thorn-EMI Electron tubes in Ruislip, Middx. The compnay has been through various hands and their current website is:
http://www.electron-tubes.co.uk/ There are data sheets freely downloadable which may include some of the historic types that we may encounter.
If that source of data fails I have an EMI PMT data book from 1970. I have occasionally scanned entries where members have needed specific data.