Canon Mark III do you mean Canon 1D Mark III or Canon 1DS Mark III or Canon 5D Mark III ???
In any case CS 5 ACR update 6.7 should handle all those cameras.
Camera Raw 6.7 Update
This new version of the Camera Raw plug-in replaces the original Camera Raw plug-in that was installed with Adobe® Creative Suite® 5 or Adobe® Photoshop® CS5 software.
Support for the following cameras has been added in this update. Visit the Camera Rawpage for a complete list of supported cameras.
- Canon EOS 1D X
- Canon EOS 5D Mark III
Supported camera models
Thank you, I couldn't find that plug-in; it worked perfectly... I'm excited to do some photo-editing!