This film is available on both Region 1 DVD and Blu-ray from Kino Lorber.
You've seen Guy Standeven in something because the man was in everything.

Dear vitch: HI. The only thing I wish is that my MCA Video U.S. tape of 'THE BLACK WINDMILL' was in W/S.
But I reckon you can't have everything . . .
-CG

I reckon the only alternative is to find a DVD player here in the
USA that will play Region 2 disks.
Nero Vision will convert PAL to NTSC and you can burn it to DVD-R or DVD+RL as you please. Instructions on the Web. Another program called "AnyDVD" from Slysoft will let you play R2 discs and convert them through NeroVision without all the Region and format nags - and more info on that is available on the Web too.
For the immature among us tempted to flag this as somehow inappropriate, it should be noted that it's aimed at people who buy the UK version because it's not available in North American and would actually like to WATCH it.

It is available in the USA, but only on video. MCA released it in 1986.
Maybe Universal figured that because the movie was filmed in England they ought to release it on DVD over there and hope it would sell.
I'd be very surprised if Universal released THE BLACK WINDMILL over here on disk. Way back when it was first released on tape and for many years thereafter the VHS retailed New at $59.99.
You can, however, now go to Amazon and buy a VHS of THE BLACK WINDMILL.
I reckon the only alternative is to find a DVD player here in the USA that will play Region 2 disks.
-CG