I’m honestly surprised that Warcraft didn’t go ham on supplying 2H katanas considering how popular they are as a weapon type. It seems there’s only 2 two-handed katanas in the entire game. Both hard to get. Duskbringer seems the easiest, but it’s too low value for anyone to farm and sell on AH. =(
There are more than two. Although i could be thinking of one handers. I will have a look later.
All 2-handed Katana style swords:
Archaic Defender BoE- world drop from level 30ish mobs in Eastern Kingdoms/Kalimdor or by trade/AH.
Blade of Hanna BoE - Drops from Vanilla raid mobs or by trade/AH.
Boneslasher BoE - Razorfen Downs’ mobs or by trade/AH.
Duskbringer (as you stated) BoE - Shadowfang Keep mobs or by trade/AH.
Emil’s Brand BoP - Insane Druids’ quest reward. - Ashenvale.
Frost Tiger Blade BoE - Blacksmith or by trade/AH.
Headstriker Sword BoE - World drop off level 15-51 mobs in Eastern Kingdoms/Kalimdor or by trade/AH.
Helboar Carving Blade BoP - Testing the Antidote quest reward. - Hellfire Peninsula - Outlands.
Mo’grosh Toothpick BoE - Mo’grosh Ogres - Unobtainable except by trade/AH.
Shin Blade BoE - Drops from Vanilla raid mobs or by trade/AH.
Strike of the Hydra BoP - Aku-Mai - Blackfathom Deeps.
Ta’Kierthan Songblade BoE - Lord Darkscythe - Eastern Plaguelands. Unobtainable except by trade/AH.
Typhoon BoP - Only obtainable from Wow Anniversaries via Azuregos, Dragons of Nightmare and Lord Kazzuk (Shared loot table). My personal favorite Katana.
I may have missed some but think I got them all. Hope this helps!