Ninroot and Leyawin go hand in hand.
You'll find tons of them around the perimeter of the city walls and tons more exploring the surrounding swamps. Like
stoffe said, ectoplasm is the nice residual goo ghosts and wraiths like to leave when you layeth the smack down on them
The higher end alchemy shops should sell them as well, or visit one of the Mages Guild.. the 'house' alchemist tends to carry some hard to find odd-n-ends. Imperial City alchemists (Guilded Carafe specifically) should sell it too.. but not sure if it's a random merchant inventory or if it's a leveled list item.
Welcome to the endless world of stunning visuals and no sleep .. hehehe
EDIT: moved to The Outlander Club