I took my 40 Iksar Monk to Kaesora and I got this shield after being there less than an hour. I was soloing and had killed maybe 5 spec guardians when this dropped. I got lost and killed shortly after and I decided to take my 48 Necro there to see if he could clear the Library Area where my Monk died so I could then log the Monk and retrieve my corpse.
I was only there about 10 minutes and had only killed a few mobs when this dropped again for my Necro. Unfortunately, I had one in my Necro's bank from many levels ago and could not loot it because it is lore.
So I think this is a common drop in Kaesora. Or maybe I just got very lucky - twice.