hey zach, you can buy nx prepaid at: Maximus Cards - Your number one source for Instant Xbox Live Points, PSN Card, Wii Points, Warcraft Key and iTunes Prepaid
$25 = 25, 000 nx ; $10 = 10, 000 nx
check the customer reviews it you are skeptical. they accept paypal, cc, bank transfer, etc.
i buy my nx from there since i got error code 0 too. u almost get ur NX code in your email instantly.