Where can I find a Leaf Stone in Pokémon Crystal?

Question

I need to evolve my Weepinbel

Answer 1

1. From the girl who stands in the middle of an opening in the grass near the daycare in Johto. Just get her phone number and wait for her to call you saying that she has something to give you. Shell give you a Leaf Stone then.
2. From Bill's Grandfather on Route 25 of Kanto if you show him an Oddish when he asks you to show him a green round Pokemon.

Source: Knowledge and Bulbapedia.

Answer 2

Apparently, you can get it from Bill's Grandfather on Route 25 of Kanto.

Source: This.