This quest is not available in game.
Stoma the Ancient has asked that you bring him a Mature Black Dragon Sinew. Should you find this sinew, return it to Stoma in Felwood.
Vartrus may offer you the stave to create a bow of Ancients but only I can enchant the string required to complete the bow.
It is a simple task, puny one. Slay a mature black dragon and remove the sinew from its bones. Return that sinew to me and I shall enchant the material into an almost indestructible bow string.