Go to mlb.com, click on scoreboard and then click on "box" for the game you want. Scroll to bottom of the box score and they will have umpire info listed. Again, box isn't up until about 30 minutes before first pitch but plenty of time to get your play in.
I agree with you, since I started following up info very rarely will I play a game without knowing who is benind the plate and all my posted plays here are based, in part, on the umps.
Best of luck...