I'm satisfied Sharn Syndicate doesn't have one, since approximately 8 billion Artificers have run through that series with no reports.
I doubt 3BC has one since there's nothing else named there, and I suspect a lot of 'everything once on elite' toons have run through there recently with no reports.
Surely though, Necropolis has one. I'm happy to rule out Bloody Crypt and Shadow Crypt - since despite being likely locations, those end chests have probably been ransacked by many toons in the name of XP farming since U11 came out.
So, I'm thinking Cursed Crypt maybe? Given the insanely low drop-rates of other named gear in there, it's possible that not enough traffic has passed through that chest since U11 to see a single drop.
The two other alternatives as I see it are as a rare explorer drop - which is slightly more plausible given the existence of Vulsejhthgnasdfx's Gem and tapestry shreds, but rather unlikely. The final chance is Abbott, but given a lack of reports of a find, I'd rule it out.
So - the thrilling conclusion of this post is that I reckon there's a chance there's a rune arm in the Cursed Crypt chest.
Also: Amrath. Rare in explorer area drop? Else would probably get noses out of join in messing up belt/ring drops in qs/raid. Would love it to drop only in end chests of Elite A New Invasion. That would be spectacularly evil.