Trivia cards are displaid randomly in several locations of the game (only in hard mode), and it can be cumbersome to find 100 of them.
To speed up collection, here's a tip :

• Make a save at the end of the chapter 4, before getting the latest golden key
  
• Go to each game location to find trivia cards
  
• Exit the game without saving (cards are saved no matter what)
  
• Update the time of your computer and add at least 2 hours to the current time
  
• Reload your save, you'll find a bunch of trivia cards in main locations

I've been able to complete 100 cards in roughly 30 min with this tip!