Elden Ring, like any RPG, is all about progression and upgrading.
Smithing Stones are used to upgrade normal equipment up to +25. There are various levels of Smithing Stones and you need to use the correct type that corresponds with your equipment.
That being said - where can you find them? Here's where you'll want to go to buy Smithing Stones in Elden Ring.
Where To Buy Smithing Stones In Elden Ring
Smithing Stones are using at a Smelters Table to upgrade your weapons throughout Elden Ring, and more than likley you're going to gather quite a few of them during your playthrough.
If you're looking to snag some easy ones, we recommend heading over to Limgrave Tunnels, which is a small dungeon next to the starter region dragon that spawns within the lake.
However, from what we can tell, if you're looking to purchase these stones at a vendor, the only one we can find as of now sells Somber Smithing Stones and can be found within the northern region of the game.
After defeating Godrick, head north and there will be a merchant titled Smithing Master Iji, who will sell you these stones!