Professor Oak rubs his chin as he thinks.
"You're right, they are rare. It's difficult to tell were you might find each one, but some places get them more commonly than others. Miners at Mount Moon occasionally dig one or other of them up, and I know you get fire stones near the top of Cinnabar Volcano. Celadon department store tries to keep some in stock, but so many trainers want them that they've put the prices through the roof in the last few years."
He shrugs.
"Your best bet is probably to ask around. I'm not an expert on geology. Pewter and Cinnabar City both have centres with geologists and archaeologists who might be able to help."