There's another two:
- Can be pickpocketed from Dexion (Dawnguard required) It's called 'Akavir Sword', though it's no different to the standard Blades sword.
- A man in Nightgate Inn, (Forgot his name), he will always be there. Can be pickpocketed.
I was about to mention was one on the guy in nightengale inn from day one...
The first actual Blades sword can be got after conversing with Delphine after the horn of jurgen windcaller quest... is one on her weapon rack,
There is Bolar's Oath blade which may be taken from bloated man's grotto really early (not while is active within hircines quests) - Bolar's is like dragonbane in the fact it uses quicksilver to upgrade and is basically same as dragonbane but a different enchantment.
Of course is a ton of Blade swords at Skyhaven.