Don't think so.... not that I'm aware anyway. You can however customize the ones there that you have. Right click the button and click on "crop and adjust". The frame, the media mask as well as the media can all be independently adjusted. Brightness, contrast, alpha, cropping, adding effects, keyframing... etc, can all be done
You can make your own too.
Use the existing ones as guidelines and do whatever you want.
For example, I created "tooth" buttons for a dental video.
You're limited only by your imagination and creativity.