You can't buy leaf stones in emerald to obtain a leaf stone find a green shard and trade it to the hunter found on the route west of mossdeep city he will trade you a leaf stone for the shard.
i think you get it on a certain day at the pokelathon. I have heart gold and it cost 2500 points. Hope it helped!
you cannot buy a water stone
you can get it by going to route 119 at the tall grass
Go to black city and gain people from pokemon white's white forest who gives you the option of selling leaf stone. After, save, go to the market that just appeared in your city and buy (expensive) leaf stones.
You need to buy it from Kecleon stalls in dungeons.
Go to liyovile city and then go to the general store and buy it
Go to the Celadon City department store and buy one.
The fastest way is to earn points on the Pokemon-a-thon and buy a Leaf Stone there for 2500 points. The Leaf Stone is available at Thursdays I think. You can also get a leaf stone from Bill's Grandpa if you show him an oddish, he is just above Cerulean city. and you can find a leaf stone in viridian forest.
You can buy them on the fourth floor of the Celadon Department Store
You cannot buy leaf stones you have to earn them from people like lennora the second gym leader or find them in poke balls.
If by duy you mean buy then the answer is you can't. The only Pokemon games where you can buy evolutionary stones are Pokemon Green, Blue and Yellow (that's right, the originals).
you can buy Pokemon emerald, ruby, sapphire, firered and leafgreen at gamestop
Buy it in Mystifying Forest in the Kecleon Markets for 1000 Poke Dollars