Hi, I hope that you have this video by now but if you have not, keep trying e-bay for the video. As far as I knew it was never released on DVD but maybe wrong. I, like you, had been looking for it for years and eventually got it through e-bay for about £15. The Green Man is brilliant and the book is really hard to find too, if you haven't read it (by Kingsley Amis) you should it's brilliant. Albert Finney I thought was perfect casting too and the ghost is so sinister. If you do not have the video by now please keep trying e-bay.
You can buy the DVD from Amazon UK.
I will be soon as I've been waiting for it for years.