Huge group of them close to the East Lough Derg parth farm. From the stables at the farm go past the field of parths and up the hill on your left. Most of the time there is a Dergan on the hill.
I do not know where else they are located, but I bet there are 30 of the little beasts at this spot.
Fast little devils:( I can solo a yellow 75% of the time... If theuy resist and get in range to cast their eath spell or whatever it is im mostly screwed, nice xp though:) Svante lvl 18Eld