If you haven't found any Blood Stone Chunks around the areas you are exploring, you likely just need to advance further into the game. The first one that you can find in the main story areas is in the Forbidden Forest with areas after that having progressively more and more available. Additionally, you can farm Blood Stone Chunks from
the Skeletal Scourge Beasts in Yahar'gul, Unseen Village and the Scourge Beasts with blue eyes in the Upper Cathedral Ward. The blue eyed Scourge Beasts in the Upper Cathedral Ward are faster to get to, so they are generally your best bet for farming chunks.
If you go to farm Blood Stone Chunks, be sure to equip an Eye Caryll Rune if you have one available, since it will make it more likely for the mobs to drop items.