Most affiliates living outside US will have contacts within US. Email contacts. Facebook contacts. Twitter contacts. They can advertise in International Magazines such as Time, newspapers circulating across the US such as the New York Times or the Wall Street Review, list on Craigs List or use banner ads on websites.
This is a very attractive product and with 300 million people in the US, there should be no shortage of buyers and with the also attractive commission no shortage of sellers.