If the OP will have any U.S. currency, there should be some vendors selling wrapped, pre-valued $5.00 Metrocards (no $1 new-card fee) at the Jamaica AirTrain station, on both sides of the faregates. I would buy one of those for cash, and then try to add the seven-day pass at one of the Metrocard vending machines there, or at the subway station below, using either cash or debit/credit cards.