I don't know a lot about lost media, so I only added a few notorious examples that I've heard of. I'd like people to add responses of lost media that they find interesting. Please make your responses as specific and unambiguous as possible.
I will resolve options as YES only if the material is not only found, but also made available publicly.
If parts of a piece of media are found (e. g. half of a Doctor Who episode) I'll resolve to a percentage. I will not count finds that are not the actual media form that people are looking for (i. e. stills of a movie instead of footage, sheet music to a lost song instead of the original recording etc.). I will count finds that are of lower quality than the original (e. g. a screen recording). These will resolve as YES, not to a percentage.
If there's any ambiguity about whether the media found is not the real thing, I'll see what the consensus on Wikipedia and the /r/lostmedia subreddit is.
I'm not an expert, but judging by the wikipedia page the BBC could easily pay people who have episodes in their private collection, but are unwilling to do this.
Normalize rewarding desirable behavior monetarily.
https://en.wikipedia.org/wiki/Doctor_Who_missing_episodes
https://manifold.markets/asmith/will-any-of-these-six-lost-films-be
See also my related market Will any of these six lost films be rediscovered before November 2026?
The Story of the Kelly Gang (1906)
A Daughter of the Gods (1916)
Cleopatra (1917)
Hollywood (1923 film)
Convention City (1933)