More specifically, what is the difference between a blunder and a mistake? And how does Chess.com decide that?
Essentially it is just a numerical evaluation change, the higher it is, the more likely it is considered a blunder. I don't believe the site has released details on the magnitude of change that makes one move a mistake and another a blunder.
I think there is an official informational thing somewhere on chess.com. I could be wrong, but I believe its roughly inaccuracy is a change in evaluation between the best move and the one you played of +/- .33 to 1.0, mistake is something like +/-1.0 to 2.5, and blunder is more than that. However, I believe the chess.com system does take into account the game situation. For example, if the engine evaluation is like +28, then an evaluation difference of +/- 4 may not be called a blunder.
If you are looking for games where blunders are most likely to occur
.....just check my archive. There should be plenty of examples, unfortunately. 
I'm looking to analyze chess games to find when blunders are most likely to occur. In order to do this, I would like to be able to detect blunders from a change in the point system?
I know that blunders are subjective, but would like to have a way to detect them automatically.