Customer and Border Patrol
Border Patrol is just a small part of the Customs and Border Protection (CBP) agency. CBP mainly inspects people and goods that come into the U.S. through any port, whether it's by land, sea or air. So they have officers all over, and intercepting counterfeit imports is part of their mission. Immigration and Customs Enforcement (ICE) is the other agency within DHS that has boots on the ground to find violators after they get past customs. They should be part of a task force to find illegal imports as well.
Border Patrol is probably what you're thinking of, they are the ones actually patrolling the border. Or are you thinking of the TSA, which is yet another part of DHS?