Xbox Live has listed the "Merc With A Map Pack" downloadable content as available for purchase. This is the same map pack that is a pre-order bonus for GameStop. This will most likely be available on PSN soon as well. The DLC is listed at $3.00 (240 MSP). [SOURCE]
The Deadpool video game comes out 6/25/2013.
More Deadpool video game news can be found here
The Deadpool video game can be pre-ordered here