I wasn't aware of "This Mad World of Ours" (1966) but it's listed on this John Denver Discography. Looks like the albums from the John Denver days of the Mitchell Trio were:

• 1965 The Mitchell Trio: THAT'S THE WAY IT'S GONNA BE
  
• 1965 The Mitchell Trio: VIOLETS OF DAWN
  
• 1966 The Mitchell Trio: THIS MAD WORLD OF OURS
  
• 1967 The Mitchell Trio: ALIVE!

I believe the Mitchell Trio Songbook is out of print, but readily available as a used book at Amazon or at Bookfinder.com. Looks like the going price is about 25 bucks, but Amazon has a couple for under $17, including shipping. Search under Mitchell Trio Song Book and also under Mitchell Trio Songbook. More about the Mitchell Trio Song Book in this thread (click), as we call it.... ;-)
-Joe-