I was cleaning out my pantry and found my stack of various pizza stones and kiln stones I had when I converted my grill to a pizza oven.
I had 2 of these Pizzacraft round stones. They happened to fit the Blackstone exactly. 16.5" diameter
Blackstone on top. Pizzacraft on bottom.
They are almost .1-inch thicker. Not a HUGE difference, but it can't hurt to have a little more thermal mass on the bottom (or if I crack the stone).http://www.amazon.com/gp/product/B005IF2ZNM/?tag=pizzamaking-20