Hello SGalHC,
Thank you for contacting us. The “Template” options listed under “Page Attributes” are based on what the theme offers.
The easiest way is to use elements from other themes on a page is: Create a new page, then click the “Add GridBlock” button next to the “Add Media” button. This will allow you to choose the pieces of the other Themes that you want to use and easily add them to the page.
Alternately, you can customize the Template Hierarchy to add additional options. Keep in mind this will require you to develop a custom solution.
Thank you,
John-Paul