General Song is one of your missions. You must do all the missions for the Spades, that gives you enough info to go get him. You go to the DMZ and talk to the guy for the Ace quest. Once you get there just follow instructions to find out where he is. Hope i helped :)

No!! Not the DMZ, for the Ace of clubs and Dimonds its the DMZ for the others, its Kusong in the northern Province

Collect enough intel from members of the Deck of 52 (80 intelligence points needed) and then go to Allied HQ and accept Song's contract. You will then be inserted into a large North Korean base, the one with Song's nukes.
NOTE: You don't have to complete all the Spades contracts to unlock the Song contract.