In order to reach +10 on a weapon, you will need these materials:
- 16 Blood Stone Shards
- 16 Twin Blood Stone Shards
- 16 Blood Stone Chunks
- 1 Blood Rock
All iterations of Blood Stones can be found through various areas in the game, the enemies that drop them consistently are the small skeleton bug-like enemies that are basically the crystal lizards from the previous Souls games. However, there is only one guaranteed spot in the entire game where you will find a Blood Rock.
*** Spoiler - click to reveal ***From the "Mergo's Loft: Middle" lamp, head up the stairs and continue forward until you see a caged elevator to the right. Take it down and face the building, as you will have to roll out of it before it stops. You will see an open window shortly after it begins its descent that you need to roll into.
The following area is littered with enemies that can induce Frenzy, so carry many Sedatives and wear any gear/runes that increase Frenzy resistance. It is a pretty straightforward path that eventually leads to a lever. A cutscene will play with a giant monster being dropped down a pit inside of a tower, drop down the hole in the room and head outside. You will be able to drop into that tower, where the Blood Rock will be on a dead body.