My imagination runs amok..
There is a Disney+ but https://disney.fandom.com/wiki/Little_Dog_Lost is not on it. Nor is any other Walt Disney's Wonderful World of Color or whatever name the anthology ran on television since 1954 but to me this is the only one that matters, what can I do, I love corgis :)
The Mists Of Avalon mini series from 2001 is nowhere to be found.
Many, many movies have been made out of the novel The Count of Monte Cristo but what many consider the closest to the book, Robert Vernay's version from 1954 with no less than Jean Marais in the lead is impossible to find these days. This was Vernay's second Cristo movie, the vision he always wanted to make but couldn't in 1943 when he made the first. But no one knows of it because streaming, DVD, whatever you want just doesn't exist. Rare Films And More sourced a high quality 16mm print (it's in German) and digitized it and wrote English subtitles for it -- but it's a pirated copy, I don't think it entered the public domain yet.