The best place to start looking is at the Eastern Province Pokémon Center in Area Two and down the river. Throughout the River Bank, you will find many items, including Stone in Pokémon Scarlet & Violet.
Eastern Province Area Three, in which you might find some Fire Stones if you collect enough items, as they are for draining.
Fire Stone can also be purchased from Delibird Presents stores after taking out three Gym Leaders.
This is all you need to know about where to find fire stone in Pokémon Scarlet and Violet, so we hope we have been as helpful as possible.