I'm not sure if people follow up on the hidden skins or have read the recent post on Mmo-champion, but some stuff has been discovered for a variety of classes regarding hidden artifacts. A lot of stuff has been datamined for the Corrupted Ashbringer, and it seems to tie with the old "real way" to get the ashbringer. You need some books and a whole lot of other stuff like Nefarians head. Now you can't sell nefarian's head, but you CAN sell the books.
The books are: Nat Pagle's Guide to Extreme Anglin' and A Thoroughly Read Copy of Nat Pagle's Guide to Extreme Anglin'.

The first book can be looted from DM in A Dusty Tome. They're laying on the floor around in DM. If you want then you can use Yeti Radar Bot to find them.  There's a great comment in the comment section on Wowhead stating where to find the books on the ground, and there's a map with coords in the link too.
Known Spawn points:

DM North
Near the southwest corner in Fengus' courtyard
Under the ramp near which Slip'kik patrols
Directly behind the Observer

DM East
Near Lethtendris (Did this over 100 times, saw 10 Dusty Tomes, spawn rate is 10% so far)
In the big drop down area at entrance, middle along the east wall.
North end of the ledge (directly above the big door), between a pack of lashers and a big tree.
In the Shrine of Eldretharr (End of the instance, by the root that Alzzin the Wildshaper walks up to).

DM West
The Southwest corner of the first courtyard

I'd suggest going DM East...