Do you mean you are looking to acquire Dragonbane, the Ebony Blade, and Harkon's Sword?
If so:
Spoiler
Dragonbane is in Skyhaven Temple and you must do the main quest up through the completion of the Alduin's Wall quest before you can enter there and get it.
The Ebony Blade is the reward for completing the Daedric quest for Mephala, called The Whispering Door. It takes place in Whiterun and is started by talking to the innkeeper at the Bannered Mare and getting dialogue that leads you to talk to Jarl Balgruuf about his children. (Note that if you have taken Whiterun for the Stormcloaks in the civil war, Balgruuf will be in Solitude at the Blue Palace and not in Whiterun.) You must be level 20 or above to get this quest.
Harkon's Sword is carried by Lord Harkon, you must have Dawnguard installed and either pickpocket it off him or complete the main DG questline and then loot it from him after his death.
You might try looking here for info on other unique weapons:
http://www.uesp.net/wiki/Skyrim:Unique_Items#Unique_Weapons