The dragon torso stone can be found in Irithyll Dungeon near the lift up to the shortcut. It is on a stone dragon sitting in the “path of the dragon” position. If you look left you will be able to see Archdragon Peak in the distance. The dragon head stone is located after defeating Ancient Wyvern in Archdragon Peak. In order to get there, you need to defeat Oceiros, the consumed King and get the “path of the dragon” gesture from the corpse in the room behind his boss room. Once this has be acquired, head back to the place you found the dragon torso stone and use this gesture right next to it. You will then be ported to Archdragon peak. The Ancient Wyvern is just up the hill and there is a bonfire right before it. The Twinkling Dragon Torso Stone can be found after the Great Belfry bonfire in Archdragon Peak. Just down the stairs and out into the sunny area are tons of serpent men enemies. At the very end of the area, past them all, is an altar where you will once again use the “path of the dragon” gesture to receive this stone.
After acquiring the Twinkling Dragon Torso Stone speak with Blacksmith Andre and he will give you Hawkwood’s Swordgrass. After acquiring this you can travel to the Abyss Watchers bonfire in Farron Keep and fight Hawkwood for the Twinkling Dragon Head Stone. Be warned, however, this is an extremetly tough fight and he will take your Dragon Stones if you die. .
As found on Youtube