Alan,
I am afraid that is all we offer in SmartDraw. You are welcome to seek out content to import into SmartDraw from 3rd parties, although we do not have any partners in that regard. One resource you can try is Reichard Software (they do have mining symbols):
http://www.reichard.com/
I am not sure what they charge (typically it is not a cheap proposition), or if they offer content individually. Otherwise, you would want to seek out symbols in one of the following formats:
JPEG, PNG or ideally EMF (Enhanced Metafile Format) or WMF (Windows Metafile Format)
Good luck with your search.
Regards,
SmartDraw Support