Where to get a leaf stone in Pokemon FireRed?

You can't get a Leaf Stone in Pokemon FireRed. It's exclusive to Pokemon LeafGreen.

Here's why:

* Version Exclusives: FireRed and LeafGreen have some exclusive items and Pokemon. The Leaf Stone is one of those exclusives, available only in LeafGreen.

* Trade Evolution: The Leaf Stone is used to evolve Gloom into Vileplume. In FireRed, Gloom evolves into Bellossom using the Sun Stone, also a version exclusive item.

To get a Leaf Stone in FireRed, you'd have to trade with someone who has a LeafGreen version.