Summary: we got the monitor working (using a signal generator from the Seattle Living Computer Museum (thanks!)), but the display is very dim, probably due to the old CRT. Does anyone in the bay area have experience with CRT rejuvenation?
If it's really the tube, and it's a truly rare custom tube and not just something you might be able to find a suitable replacement for, maybe these guys can help:
The last commercial CRT rebuilder for ordinary TVs in the US closed in 2010.[1] But there's still a company that does it for military display devices that need to be kept going.[2] "We are your obsolescence solution now and in the future."
It really is a custom tube. PARC built the first tubes in-house (PARC was also a copier R&D facility, so they could build precision optoelectronics) but then sent the job out for production.
[1] http://www.tvtechnology.com/miscellaneous/0008/last-lone-wol... [2] http://www.thomaselectronics.com/
This is a really unique piece of hardware and of course you might want to try this technique only if you have no choice.