You can get the Ashbringer by completing Naxxramas on heroic.
No, Ashbringer is not available as a obtainable weapon in Wrath of the Lich King. Ashbringer is mainly associated with the Scarlet Crusade and was wielded by Tirion Fordring. It is a legendary weapon in the lore of World of Warcraft.
Ashbringer has an incredibly long and rich history, which was rewritten several times. Originally, the Corrupted Ashbringer could be looted from the 4 Horsemen in Naxxramas. However, the story would be fleshed out in Wrath of the Lich King, with Mograine assisting in cleansing his son and Tirion Fordring holding the Lich King at bay with the now-cleansed Ashbringer. Because of this, the Corrupted Ashbringer no longer exists and was removed from the new Naxxramas. Since Tirion Fordring currently holds the Ashbringer, players cannot obtain the item, and likely never will.
Yes it is
No not as a player weapon. It is only usable by NPC characters.
112 Ashbringer-ID#33641123 oh largest hit 158
The players, along with the leader of the Argent Crusade, Tirion Fordring. As the Lich King wields the evil runeblade Frostmourne, Tirion wields the redeemed Ashbringer.
In terms of chronological, as in the history of warcraft, the order would be:World of Warcraft (detailing what happens to Varian Wrynn)Ashbringer (detailing Darion Mograine, concurrent with the WoW comic)Sunwell Trilogy (leading up to the rise of the Lich King)Warcraft Legends (following up on the Sunwell Trilogy)Warcraft: Death Knight (unreleased yet?)Warcraft: Legends seems to be a series of short stories, so the continuity might be a bit difficult.