The system content templates are not stored, they are generated within mojoPortal code. There is no way I know of to create additional system content templates without customizing the base mojoPortal code, and we strongly discourage forking the code.
You may already know this, but you can create your own custom content templates as described in the Creating Content Templates document. However, unlike the system content templates, these are not cross-site, so you will need to create and maintain them in each of your sites separately.
Hope that helps,
Jamie