In my current campaign, I have one player with a Hobgoblin Ranger who uses a 2-Bladed Sword, for the 1st five levels he had a magical Bastard Sword (Which he sometimes used 2 handed). Around that time they found an ancient door in the bowels of Sharn that spoke of a hobgoblin hero who had been entombed below 1000s of years ago. He researched the history and found he wielded a Two-Bladed sword, then convinced the rest of the party to help him in his quest and retreived the Blade after quite a few sessions.
So the answer is I probably would not have exotic weapons placed as treasure, but they would exist as major quest items. Frontline fighters who are the only ones who usually end up taking exotic weapons, end up with pretty unique and interesting magical weapons in my campaigns anyway though so this is pretty much par for the course.