You cannot buy or play ArmA 2 on PlayStation 3. The game (released 2009) and its expansion Operation Arrowhead are Windows PC exclusives. Bohemia Interactive's Real Virtuality engine is built for x86 architecture, DirectX, and keyboard/mouse control schemes that don't translate to PS3's Cell processor and gamepad.
ArmA 2: Combined Operations (base + OA) is essential for DayZ mod (the original). Often <$5 on Steam/GOG sales. Requires modest GPU (GTX 660 / HD 7850) and 4+ GB RAM.