There's no place that tells you how to add yours on the addon/theme sites
maybe this could be useful ;) http://www.elkarte.net/community/index.php?topic=2319.0
ehm:
http://www.elkarte.net/community/index.php?board=12.0
"How to add your addon to the Addon site listing" <= the first sticky
http://www.elkarte.net/community/index.php?board=16.0
"How to add your theme to the Theme site" <= the only sticky
But, if you didn't find them, it may be they are not visible enough.
Where would you look for such informations?
On the theme/addon sites pages. I get that they're on the forum.