Castle Hill used to own it, then Westchester Films, which was acquired by Shout! Factory. As to distribution deals, it apparently varies by title. Someone else may have better details on this complicated history. Many titles have been released via Janus/Criterion (STAGECOACH, FOREIGN CORRESPONDENT, etc.).
This would make such an OUTSTANDING Criterion release! As far as thought-provoking Duke films go, this one has got to be close to the top of the list.
And really, to say this is a John Wayne film is not really fair. It is much more of an ensemble piece, in which each character gets pretty much equal screen time, with their own back stories.
European home video rights to this title are held by Studiocanal. They released The Long Voyage Home on Blu-ray both in Spain (last year, ASIN B01M24BH3Z) and in France (2015, ASIN B012E9VFLC). Apparently theirs is an older master. The generally positive review at http://www.dvdclassik.com/test/blu-ray-les-hommes-de-la-mer-showshank-films also contains a deal-breaker: 25fps. The review also mentions that a DCP of the UCLA restoration is seeing cinema bookings in the US. I am certain we're not facing a long wait toward a worthwhile Blu-ray at the proper speed.
Thanks to Eric for the link above!