Steps to Unlock & Unhide Windows 7 hidden locked Themes
1. Unhide the Windows 7 System and Protected Operating System files from Windows explorer -> Organize -> Folder and Search Options -> view tab

2. Navigate to C:\Windows\Globalization\MCT.

3. Open a MCT-(AU, CA, GB, US, or ZA) folder for the regional theme that you want.
NOTE: AU, CA and ZA regions all have the same themes though.

4. Open the Theme folder in the selected region folder.

5. Select the .theme file to use it.
NOTE: Once you select a .theme file, Windows 7 will save it so that you will be able to change or select this theme again from within the normal Personalization window location.

6. Hide the Windows 7 System and Protected Operating System files.

7. Enjoy your new regional themes!!