The most common place to find a Fire Stone in "Pokémon Black" and "Pokémon White" is within swirling dust clouds. Dust clouds are randomly encountered in the following locations: Wellspring Cave, Chargestone Cave, Mistralton Cave, Twist Mountain, Challenger's Cave, Victory Road and the Giant Chasm.
In addition, the player can receive a Fire Stone by answering "Pansear" to a question from a character on Thumb Pier, located directly south of the Bridge Gate. Fire Stones are also found at random in the Desert Resort. Fire Stones can be used to evolve the fire type Pokémon Vulpix, Growlithe, Eevee and Pansear.