There's a few items still "Missing", such as these and half the Artful-Dodging set.
I'd wager if it's not a high end mythic drop somebody would have found it by now, on live if not on PTR.
Unless it's from some incredibly specific set of events (such as to get the coin purse) then there's enough players to have come across some of it, even by accident.
Honestly, I half think Blizzards not quite got around to adding them yet, and they'll be hot fixed in a later patch. I actually think it's likely some of this stuff was tied to the Order hall items that allowed you to pickpocket other players. The items were removed pretty late on last minute, so maybe they've just not added a different method to get them since.