Baeleon and Keladry,
Like I mentioned before, Dure'dhel accidentally learned in past that the Unicorns used to lived alongside the Mystic Wood Elves of the Autumn Woods, but I unfortunately know little other than that. Further unfortunately, the Autumn Woods are deep into Corrupt territory at this point and all of the true Children of the Autumn Wood are permanently dead, so a lot of information from that part of the world has become somewhat extinct. Mesa the Watcher is somewhat tied to this world still, but with the whole Wrathgate situation, you'll agree that it isn't exactly easy to get in contact with him currently.
If the Mist Caves were still around, that would have been my first thought of where to go, but those closed up years ago.
Maybe a Spirit Farewell targeting one of the spirits from the Autumn Woods might help? I don't think that a Spirit Farewell would function on Mesa right now, so you'd have to find out the name of a different one, as well as confirm that they died no further back than however far back Asher can cast the ritual. Even if you found a name, though, it'd be hard to know whether he or she would be a good source of information on Unicorns. You'd hate to find a name and cast the Spirit Farewell only to learn that you found the name of the Autumn Woods' town drunk.
Maybe a Lore ritual targeting the vine might help? Lore rituals have been known to sometimes give the caster insight into the history of a target as well as its current properties. Dure'dhel once empowered a Lore with so much energy that it temporarily summoned a Mist Guardian that told him about the targets of the ritual, though I can't guarantee that such a thing would happen again if attempted.
Maybe Node Delving for information on the state of the Unicorn spirits in the Autumn Woods? That's a sort of dangerous route, and it shouldn't be attempted without at least one person that can shrug off the Weave's commanding influence while doing so, but it has been known to provide quality information in past.
I'm sure there are other options that haven't occurred to us yet. I'll keep thinking and let you know if anything comes to mind.
May the Light guide you, the Shadow guard your path, your Words have Power, and your Memories be Knowledge,
~ Gandian Ravenscroft
Magus of Tempered Rage
