Is one of these the page you need?
Which operating system are you using?
Have you tried Help>Updates from within photoshop cs6 to get either camera raw 8.3 or 8.7.1, which should enable photoshop cs6 to open the canon 5D Mark III files.
(version of camera raw depends on your operating system)
If that doesn't work try one of the following camera raw plugin installers:
Camera raw 8.7.1 plugin
If you have windows xp or vista or mac os x snow leopard (10.6.8), then you'll have to use the camera raw 8.3 plugin installer: