Finally found the 'grit' ingredient for my gritty mix.
Much thanks to cebury for locating the source for me, THANK YOU CHRIS! Even though he lives 2 hours away from me.
I got 2 bags of the Manna Pro Poultry Grit, 25 lbs, $7.80/bag. There's no indication of grit size on the bag, so I just felt with my fingers, seemed about right. Does it look OK to you gritty mix experts?