To what are you referring when you ask about "add-ons to Premiere 13" (assumed you mean Adobe Premiere Element 13)? On what computer operating system is your Premiere Elements 13 running?
Premiere Elements has not come with a Content Disc or offered Content download from an Adobe web site since Premiere Elements 10.
If "add-ons" to you mean Content download...DVD Templates, Movie Themes, Clip Art, etc....then most of that is going to come from downloading
Content from within the opened project. There is a limited amount of content that comes complete as part of the installation.
A description of this process is fully described
Any questions or need clarification, please do not hesitate to ask. Please supply more information If I have not targeted your question.