You know Virbank City? Go South from there, and you will go into the Virbank Complex (But you need to go even further South from there, as Growlithe is only found in that part). There are some trainers, and you can find Pokemon there such as Growlithe itself. You could also find Elekid there, in case you like it or it's evolutions. But anyway, in my opinion, the best place for finding Growlithe is to search in the Dark Tall Grass hidden in the middle East, because you can encounter two Growlithes at once!
As for the Fire Stone, I searched on Bulbapedia, and it is hidden. That means the Dowsing Machine needs to be used to get it.