Mine was from the Limenauruus (WB) at Tribune's Folly. Together with a lead for Belharza's Band.
German Version, PC EU.

Treasure chests for me also but it seems to be a rare drop because I've only gotten it a few times.

I'm also pulling out my hair over the lead for Echoes of Aldmeris from Auridon. Info states it drops only from chests and I have gotten it once but I've been trying for several years now and nope to a second drop. I love this item and want to be able to buy it for all my houses but I can't even get a second drop let alone a third! This is absurd, none of these should be THAT rare!

Got the Dibella Shrine lead today from a treasure map chest (Gold Coast I).
Echoes of Aldmeris droped once for me. Treasure chest in the wild, back in march this year.
btw...
my experience is, that vary things i'm doing - change what i do, the way i do it, or just do things at different times - is better than listen to Captain Ahab, sitting on my shoulder and whispering something about a white whale.
There's nothing wrong with farming, if you're in the mood for it. But even then... for example, not long ago i was on the hunt for a lead from treasure chests, too. Opened some dozen on the map till it was time to logout. But instead to port to my "base" from where i normaly start my routine the next day, i loged out beside the last chest i opened. Next day i loged in, the chest was there again and - bingo.
Sure, especially 2nd and 3rd drops can be really not grabbable (that's what rng stands for, right? ). So i always try to be prepared for the right offer from filer Ool. That's a fine thing in my opinion.
However, wish u all good luck, too!