I think it's very unlikely that someone with a complete, decent quality lost episode is just sitting on it. It's more likely that any existing tapes are poor quality, degraded, or partially recorded over. Or even that the hardware to play it back doesn't exist anymore.

IIRC, Betamax came out in the late 70s, and equipment before then wasn't really home-use friendly. Not many people had the equipment to record, much less the luxury of keeping the recording for the long term on expensive media.