This was a 12 inch release from 1987. Doesn't appear to be available on the Cavandish site.
The album you requested appear in their site in the cd - A CASE FOR GUITARS
CAVCD 8 (Tracks 1-19)
search.cavendishmusic.com/track/CAVC0008
discogs.com/Tim-Renwick-The-Guitar-Story-/release/5799774
They somehow included in the cd in addition a few more tracks, maybe some commentary music.
I have a few of those CAV 100's on vinyl if you need me to dig it out. Sounds like the CD is the way to go though