Not really. Support is user-to-user through this forum, so there's no central list.
The best way to find out is to search for a template name in the forum and if you find a thread with a lot of entries then that will be a support thread.
Also worth mentioning though that the vast majority of questions that people ask about templates are not actually specific to a particular template (though they're usually phrased through inexperience as though they are).
Instead they are typically general to how Zen Cart works irrespective of the specific template used and already answered either in the FAQ or the on the forum, and there are a lot of people who can and do answer those general questions.
So, as long as you're using templates downloaded from this site, I wouldn't put too much emphasis on whether or not there's author support for the specific template when making your choice.