Where to find the weapons: (SPOILERS FOLLOW!!)
.
.
.
.
.
.
.
.
.
.
1. Blackrazor - haven't a clue
2. Sunblade - in a tavern at the city gates. Look for a secret door. Prepare for a fight against a lich.
3. Celestial Fury - in a house in the Temple District. Prepare for another tought fight (or two
).
4. Dak'kon's Zerth Blade - (can this be used by Aerie?) Sold by one of the bonus merchants (Deidre in Adventurer's Mart). Needless to say you'll need the bonus merchants installed.