Dragon bolts (unf) are dropped by adamant dragons, rune dragons, and Vorkath. They are used on feathers in order to create dragon bolts. Doing so requires a Fletching level of 84, and grants 12 Fletching experience per bolt.
Dropping monsters
Monster Combat level Quantity Rarity Adamant dragon 338 15–40 Rune dragon 380 20–40 Vorkath 732 50–100