Where can you download the template used on the www.joomla.org site?

From Joomla! Documentation

The template used on http://www.joomla.org was developed specifically for us, and will not be released for download. We would like to maintain the uniqueness of our sites, hence the decision not to release.

The same goes for the templates on all official Joomla! Websites. They are not distributed and are not available for download. They are copyrighted, and cannot therefore be used anywhere else.