There are a couple of issues you are facing here--one is that fonts used in templates have to be available to the end user, so they must use a font that can be downloaded for free and the source of that downloadable font has to be reputable enough that the designer believes that the font will still be available in the future.
Another issue is that fonts like Helvetica and Open Sans are used often because they work well in many situations. You may consider them overused, but I might consider them perfect because they evoke a feeling that my company has been around for a while.
And of course, you have given us no idea about what type of templates you are looking for. Are you looking for a resume template for a young graphic designer, a template for corporate letterhead, a template for a concert poster? Each of these templates are going to use completely different fonts.
Are you purchasing templates, or using free templates? That might make a difference-someone who wants to sell their template might use a more unusual font to help attract more purchasers. Personally, I don't think I have ever purchased a template (not that I have purchased many) that used a font that I didn't have to download because it was not a standard font.
And then, maybe this is obvious, but you are purchasing a template--if you don't like the font, find another one and use that instead.
Okay, with all of that said, I would try looking for templates on sites that are more focused on art and design--the two that come to mind off the top of my head are Behance and Deviant Art. It is not as easy to find templates on these sites, but they are there, and it is more likely that the designs posted on these sites will be artistic or graphically interesting than those on a template site that aims to appeal to non-graphically-inclined corporate users.