You can locate the email and newsletter templates by selecting your "Resources" tab at the top of your dashboard, and selecting "Email & Letter Templates." You can also select this link and go directly there.
You can quickly navigate to a specific holiday month, or to general and email series templates with the search column on the left side of the page. Once you find the template you are looking for, simply copy and paste the contents into the body of the email or newsletter you are producing with your own service, and then modify as needed.