You can win NC from the Qasalan Expellibox, although I don't seem to be able to locate it right now, I'll put a link up when I find it
There: http://ncmall.neopets.com/mall/shop.phtml?page=giveaway Plus the NC bonus that you get for making a new account and the random giveaways during certain events (I know that there was some given away during the advent calendar and during Rosie's schtick). Unfortunately it's nontransferrable, so you can't hoard it all on one account or something, and there's no way to get giftboxes with that NC.
You could also use paypal to buy NC if you have a paypal account or if you only have nps you could wait until you get to level one and can use the black market
shhhh, keep the blackmarket on the blackmarket you can also use a credit card. but i would suggest buying the cards, since they come with free virtual items. i have seen the cards at target.