There are usually traders with a trust history on the #bitcoin-otc marketplace who will sell bitcoins for moneypack.
 - http://bitcoin-otc.com/vieworderbook.php?notes=moneypak

Because MoneyPak is irreversible, you want to trade safe:
 - http://en.bitcoin.it/wiki/Secure_Trading#Use_Bitcoin-OTC
 - http://wiki.bitcoin-otc.com/wiki/Using_bitcoin-otc#Risk_of_fraud