I know AoTC and ROTS have a hard time restoring the film versions of their theatrical release, as there’s never been a Home release of them (they’re all based on the digital versions), and I haven’t heard of anyone acquiring a print to make use of for restoration work.
I think there’s been attempts to restore The Phantom Menace, but I can’t remember the name of the project. Sorry if this wasn’t too helpful, but I figured even a vague answer would be better than nothing.