One would assume that access is given to Customs & Dept of Homeland Security too. Some of the NSA leakers think this is wrong, but I have not heard any elected government official state otherwise.
Someone leaks information about PRISM, and the primary response is TREASON! TREASON! ARREST THE TRAITOR AND DEAL WITH HIM!
Given that, do you really expect that A) random border agents are in on it, and B) feel free to just randomly disclose that sort of surveillance to someone who has no need to know about it?
Snowden had proof and plenty of it. A random border agent that finds some documents on his desk in the morning, to be used that day, does not have much proof.
Secondly, a lot of people knew, but kept quiet. I see no reason to expect a random border agent from talking, given it took years and someone like Snowden to finally talk.
Someone leaks information about PRISM, and the primary response is TREASON! TREASON! ARREST THE TRAITOR AND DEAL WITH HIM!
Given that, do you really expect that A) random border agents are in on it, and B) feel free to just randomly disclose that sort of surveillance to someone who has no need to know about it?