That was the one previously only available with a code you got if you bought the SRIV strategy guide. I'm actually a bit more happy to see that it's no longer exclusive to that. That leaves players with only two known DLC's that are potentially exclusive: Valve's TF2 items, and Gamestop's Warped Weapon Challenge gun, the Polarizer. I really didn't see this one being released separately, so my fingers are crossed the Polarizer will be eventually as well.
TF2's doubtful, since SRTT's TF2 heads still aren't.
But on the note of THIS DLC. Looks awesome