Alan is a character in Pokemon Omega Ruby and Alpha Sapphire, not in Pokemon Silver. He's the leader of the Pokemon League in those games and gives you a Mega Stone (the Mega Stone for his signature Pokemon, Mega Charizard X or Mega Charizard Y) after you defeat him.
In Pokemon Silver, there are a few ways to get a Fire Stone:
* Find it in the wild: Fire Stones can be found in the wild, randomly. Some locations where you might find them include:
* National Park (after you defeat the Elite Four)
* Cianwood City
* Trade for it: Some trainers might be willing to trade you a Fire Stone.
* Buy it: You can buy a Fire Stone at the Pokemon Center in Goldenrod City if you have a certain number of badges.
I hope this helps!