Hollywood - the 1980 Kevin Brownlow silent film documentary series that remains stuck in clip licensing hell.
Around 2006 there was going to be a Region 2 DVD release from Network, under official license from Fremantle/Thames, but it was pulled just before street date because the proper licensing wasn’t obtained for the film excerpts. Some copies got out, I know this because I read a forum post from someone who obtained a copy, but over the years I’ve never heard anything else about anybody else having copies. It remains listed on Amazon.co.uk, but I’ve never seen a third-party seller offering a copy.
I hope another escaped copy of that Network set turns up someday, because it would actually be in its native PAL. Otherwise, the best copies are the U.S. laserdiscs from HBO, but they are NTSC conversions.