Have you tried
http://www.videodisplay.com/html/chroma.html ?
Chroma Video is their replacement TV CRT division, still out of the same location in PA. It looks like they don't list the tubes any more, you'd have to call them. They may be selling off their stock of the old 25V tubes. I ordered one about 3 years ago, cost around $95 including FedEx shipping, and they didn't want the dud back.
Mike