Only one of which is relatively common.
The uncommon way would be to win a tournament (poker or blackjack etc) that awarded the NCV chips as the prize.
The normal way would be for you to receive a letter from the Palms telling you that if you schedule a trip, you can have X number of NCV chips to play with when you arrive. Any that I have ever been able to get came from players who received the offer.....but don't play table games.
Go figure.