Okay, this is killing me.
Here's the bottom line...
1. If you download the BlackBerry JDE (from RIM website), you can get and see all available themes for all models.
2. The 7100 themes cannot be run on the 72xx models.
3. The only non-standard themes for 72xx models are:
-net_rim_theme_vodafone.cod - The 'ugly' red theme
-net_rim_theme_blackberry_large.cod - The 'visually impaired' theme
4. These themes can be installed using the Application Loader, but you need to edit the Blackberry.alx file for the Loader to pickup the .cod file. (Scroll down to the these section, and follow the pattern).