In reply to philipjardine:
I spent a while earlier this year trying to find it too; I watched it when it was on BMCTV and it was fantastic. I had in mind it also used to be on Vimeo for purchase but only the trailer is there now.
I noticed back then that there was a comment on Mike Cheque's website suggesting it was going to be made available, but I can't see it any more.
I emailed Mike previously to see if this was available anywhere, but I since gather he had an accident last year so totally understandable I didn't hear back.
As UKB Shark said, it might be that the BMC are involved in getting it onto Youtube, however there was a comment on an article about it from Alex Messenger about it back in 2016:
"Alex Messenger(staff comment)
09/12/2016
After letting us host Stonnis, Mike has decided to sell it as a download to raise cash for his latest project. We wish him the best of luck with it."
(From https://www.thebmc.co.uk/exclusive-bmc-tv-premiere-celebrating-iconic-crag-... )
If you do find any information on where it can be purchased, I'd love to know - I was singing it's praises it to a friend after a trip to Black Rocks a while back and wish I could get a hold of a copy.