You might check with these guys.
http://www.hawkeyepicturetube.com/
For vintage color stuff, they are the last remaining shop. I used them on a 60's era color tube, and they were great to deal with.
Since your tube is blue only, it is technically monochrome. For this reason, and also since it's so much newer, you probably have other options, but I don't know what they are. Good luck.
John
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