I think the radar tube you are referring to is the one used in this:
http://www.earlytelevision.org/12ap4_substitute.html
Even if more shells could be found there is presently no company that will turn them into P4 tubes.
The graded seal method has been done successfully in the past, but, again, there is no one around to do it now.
RACS had problems with cracking around the anode connection when they baked the pyrex tubes and gave up on doing them.
I am convinced that with the right glass and some experimenting that we will be able to rebuild prewar tubes someday. But that is months or years away.