Dear Charles, The only source I know is a rock shop here in Florida.
Here goes: William Harris rock shop, 1118 Snead Ave., Sarasota,
Florida 34237 (941)366-6608
Bill is very hard of hearing, but wife Hilda has alot of grooved cabs
and can help you over the phone. She is from Peru and gets the
grooved stones there, as they use them for wirewrap. Her cryscolla is
very nice. Please note that most of her grooved stones are teardrop
shaped. Hope this helps, Suzanne