In Windows 7, there are (so far as I can tell) five full region-based themes available. These regions being considered as Australia, Canada, United Kingdom, United States and South Africa. Each theme includes several wallpapers related to the region.
When installing Windows 7, the very first screen you’re presented with allows you to select your language and time zone. From this information, Windows determines which single regional theme to enable.
Through a bit of messing around in the registry (always fun!) I have found how to enable all of the themes and display them in the Windows Theme Manager.
I have created a zipped registry script that will display all regions under the Aero Themes section of the Personalization screen, accessible through right-clicking on any blank area of the desktop and selecting Personalize from the menu that appears.
This is the zipped Registry Script: Download Registry Script
To install the registry script simply open the downloaded zip file and run the included MCT.reg file in the folder, responding yes to any prompts.
If you wish to play with the theme files themselves, or access the wallpapers, the theme files and their corresponding wallpapers are located in: