Rebuilding CRTs is possible at the small shop level.[1] There's still a commercial service that does it. "We are your obsolescence solution."[2] It's not cheap, and most customers are rebuilding tubes for military systems that still use CRTs. This is likely to be too expensive for video game restoration.

[1] http://www.earlytelevision.org/crt_rebuild.html [2] https://www.thomaselectronics.com/repair-overhaul/