I have one track of his on a compilation (if memory serves), Because of You (may be a demo because it sounds very rough), and I've been meaning to track down his album(s)
Seconded. Two of the best LP's by rock bands ever. Not sure they quite fit with the OP's criteria, though. I'd add 'Spirit of '76' as being as good as 'The 12 Dreams...'.You might want to try some Spirit. Start with "The 12 dreams of Dr. sardonicus".
Also, try the Zombies "Oddysey & Oracle". Now that truly is a hidden gem.
Chris