Go to the Myconid Caves of The Lesser Faydark and search out the nursery where the Lesser Amanita grow.
This is accessed either from a well in the Glade of the Unicorns ( 269, -24, -173 ) /waypoint 269, -24, -173 or via the tunnel under the waterfall in the The Fugutr Tribe area. The well access places you closer to the nursery
If you use the well, be careful. The pool you drop into is the spawn location of a named goblin Melanog (59^), that can see invis.
The nursery is fairly deep in the tunnel, heading west/south around ( 456, -22, -224 ) /waypoint 456, -22, -224.
Between the pool and the nursery a side tunnel leads to heroic ^^^ area. Keep LEFT as you pass.