Head over to thekoalition.com and enter your name in the drawing. They will be sent out tomorrow. Great chance of getting one if you are not already enjoying the beta.
http://www.thekoalition.com/i-feel-goodheres-20-uncharted-multiplayer-beta-codes/
http://www.thekoalition.com/i-feel-goodheres-20-uncharted-multiplayer-beta-codes/