I did some research on the 2012 season. In real life, 2430 games were played during the season. If my calculations are correct, there were 243 instances of a player hitting 2 or more HRs in a single game. That's exactly 1 out of every 10 games. So, in OOTP, if 10 games are scheduled on a specific date, you should see (on average) one instance of a 2+ HR game. For a full slate of 15 games on the schedule, you're likely to see (on average) 1.5 instances of a 2+ HR game. It might be quite a bit of work, but you could sim a season in OOTP and add up the number of 2+ HR games. How does it compare to real life numbers?