Found this "Gae Bolga". Uh, you don't really need it. Its one trowing spear with 60 damage. But its only one in bag and very heavy, like angons. But if you really want it to collection,
1) Speak with Tiarna Faelchu mac Airmetach about famous weapon
2) Go to Dwean Fochier
3) Check a door near the guildmaster, you need look at the sky or the top corner of that door
4) Go to the shop and answer 3 or 4 question. All you need is reading wiki - i found all answers there.
5) Got it. Enjoy.