I couldn't find the Flintstones movie from 1994 anywhere but googling it I found it here https://archive.org/details/the-flintstones_202304 and you can either download it via torrent or directly. On top of it it says that the movie is CC0 which means Public Domain. But that can't really be, it's only 29 years old.
That must be pirated, or not?
The law is tricky. From Wikipedia "For works that received their copyright before 1978, a renewal had to be filed in the work's 28th year with the Copyright Office for its term of protection to be extended. The need for renewal was eliminated by the Copyright Renewal Act of 1992, but works that had already entered the public domain by non-renewal did not regain copyright protection."
I hope that’s the case here. The sad thing is that not having the rights to something doesn’t stops you from filling a claim, even scammers fill DMCA claims over original content, the movie is already down from archive.