"Silver Train" by John Paul Jones and Jon Anderson is on the soundtrack of a film called 'Scream for Help." "Mademoiselle Nobs" on the Floyd live at Ponpeii is simply a live version of the track "Seamus" from the PF album 'Meddle.'
What is your "holy grail song" that you cannot find?
For me, that song is a live version of "Chest Fever" by Humble Pie. My guess is that it's a vinyl bootleg that is virtually impossible to find. So, if anyone knows anything about this recording, please provide some details. In the meantime, maybe one of us knows something about a rare song and/or recording that some of you are looking for.