Goofing around on Amazon the other day I stumbled upon a recent fad of drinkers called Whiskey Stones. These are stones you chill in your freezer to pour your whiskey over to chill it without diluting the drink.
As any gamer worth his weight in gold, I immediately saw them and though "OMG they are d6s!"
For just $12 on amazon I picked up TWELVE massive granite d6s that put my normal dice to utter shame.
In a pinch they could be sling stones as well. ;-)