I have most of the historical numbers, or do you want this year? If it's the latter, then you can just figure it out at MLSnet.
If you want to know which MLS player currently has had the most penalty kick fouls caused, it is Danny O'Rourke (4). I thought I would save you the trouble. He is a bit lucky it isn't (5).
He's also incredibly unlucky since the Sealy and Beckham calls were laughable. Of the four penalties, the guilty parties have been Danny (2) and Danny's reputation (2).
Oh, everyone knows Danny's reputation as a d-mid. And he definitely made two "d-mid" mistakes in his first two games at center back. This apparently set the tone so that any embarrassing flop within five feet of him his a strong candidate for a penalty. He's worked so hard at un-learning his destructive d-mid tendencies that I can't help but feel bad for him when refs give away penalties based on his name.