As mentioned in a previous post some time ago, London-based Hollywood Classics Ltd. has licensed some Blu-rays to European labels, notably Soul Media which had the Blu-ray debuts of The Barbarian and the Geisha and McLintock! Soul Media also has titles never released on Blu-ray anywhere, including Hellfighters and North to Alaska (licensed from Hollywood Classics).
The library of Hollywood Classics is rather small, but they do have rights to a few other John Wayne titles such as The Alamo, Brannigan, Pittsburgh, Allegheny Uprising and -- this is the interesting one -- Sea Spoilers, which of course has never been released on home video.
So there's always the chance that Soul Media will release Sea Spoilers. It doesn't have to be on Blu-ray -- I would be content with the DVD!
It wouldn't hurt for people on this board to send Soul Media an e-mail asking for the film to be released.
If they did release the film on DVD, however, it would most likely be in PAL/Region 2 format.