The 6th skin for every weapon is tied to some item you can get, and ofc its "hidden" (probably like that murloc in Borean Tundra). Now obviously they may not be implemented but wanted to get your thoughts on where the death knight ones could be? Going by flavor text
http://legion.wowhead.com/item=13954...-the-darkening Frost DK.
http://legion.wowhead.com/item=13954...nereapers-hook Unholy DK.
http://legion.wowhead.com/item=13954...anima-of-souls Blood DK.