Einar72, we had those tubes made for collectors:
http://www.earlytelevision.org/12ap4_substitute.html
As for the availability of guns, ones for the old tubes are no longer being made. There are an unknown quantity out there - from shut down rebuilding facilities. We have been able to purchase some of them.
The other approach is to use the old gun and replace the cathode and heater, both of which are still being made, but for how long no one knows. We are attempting to buy a stock of these.