Blue dragon scales respawn by the Blue dragons in Taverley Dungeon and in Corsair Cove Dungeon, part of the Myths’ Guild, and are also obtained as an uncommon drop from Brutal blue dragons located within the Catacombs of Kourend. For Taverley dungeon, a dusty key is required to enter this part of the dungeon, but if one has 70 Agility, one can cross the pipe right by the dungeon’s entrance and arrive directly at the blue dragons’ lair. Means to counter dragonbreath attacks are strongly recommended and some food if you are a lower combat level. Blue dragon scales are used to train the herblore skill as a secondary ingredient. Ground dragonscale dust can also be acquired from nightmare zone. This cannot be bought in Ironman mode.
Scales can be ground into dragon scale dust with a pestle and mortar. Dragon scale dust is a secondary potion ingredient used in Herblore to create weapon poison and anti-fire potions.