As you know these are the rarest of them and can sell around 50k each, i have gotten 4 of them today so i tought i'd share my location. They only drop in VR5+ as far as i've been told.
Maybe you think any house would do but lately if you logout in most houses the containers won't respawn, altough the following house respawns 80-90% of the containers every time you logout.
Also keep in mind, the drop is pretty low, but don't give up, it will drop eventually.
The zone is Glenumbra, first zone for VR5-6 for aldmeri.
City of Daggerfall