That is how the pork skin/fat comes out at carnitas places. To guarantee that you get it, be at the carnitas vendor (groceries, meat markets, or one of the specialists) pretty early in the am. Not entirely sure about the grilling aspect. I suppose you could toss the scored carnitas skin on the grill. You might also go to La Unica, T&C or other places that sell lechon horneado (as opposed to Mexican carnitas) and get the chicharon. Same advice about getting there early.
Where did the pork skin at the party originate?