A work being in the public domain just means that if somebody claims that they have the copyright and sue you for distributing that work, you will prevail in court.
Restoration itself does not grant a new copyright. Other elements included in a restoration may be copyrighted e.g. new music or the graphic design of intertitles. A new translation is also copyrightable; essentially it's only the "original elements" that enter the public domain. Working around the anti-piracy measures of a blu-ray might be a crime, idk, but that's irrelevant to the copyright discussion; once you have a copy even if it came from an 'illicit' source, you're free to copy & distribute as you wish.
But yes, you need to acquire a copy first; if you can't find a work at all, how would you copy it, practically?
He streams regularly on twitch: https://www.twitch.tv/japaneseprintmaking