What was the hardest song you tried to find and were you successful?
 
For me it was Wiggle Waggle Walk - Tony Smith and His Aristocrats
I don’t know why that song has haunted me for almost 70 years, maybe it’s the sax.
Found an mp3 online and bought the 45 on ebay.
  
Runner ups were
Sea Shell Sherry - Jerry Keller
The Little Blue Man - Betty Johnson
Ribbon of Darkness - Bill Black's Combo
I found all 3 on CD