It seems like there is no way to filter the widgets for the ones that are available for mendix native. Requesting such a Filter sounds like a perfect topic for the Idea Forum.
Here's the idea ;)
also using the search field you can look for something specific and then filter but unfortunately not from the appstore screen itself
Currently, from R&D the widgets are provided via the Native Mobile Resource package and through the Native Mobile Quickstart app.
However, feel free to add you own cool widgets. The Mendix 8.3 release contains some new nice features