Operation Arrowhead, British Armed Forces, Private Military Company and Army of the Czech Republic make up the Complete Collection. It's available right now for PC.
"For one price you receive 6 campaigns and countless single player and multiplayer scenarios spread across hundreds of square kilometers of Chernarus and Takistan maps."
"DayZ Mod requires Arma 2 and Arma 2: Operation Arrowhead to run, plus Arma 2: Private Military Company to display all textures in the highest quality - all are included in Arma 2: Complete Collection." The Arma 2: Complete Collection is listed on the for £24.90.