Marjami also has a camp full of rabbits and flytraps just south of bivouac #3, not bad since these are linking enemies and definitely less camped.
Yorcia enemies are the same level as Marjami, and being mostly plants/vermin, will link extensively. On top of that, the areas are generally packed tightly with enemies so aggroing many should be simple.
There's no easy way to get there, but in Outer Ra'Kaznar, just north of the NW Lair Reive is a large room full of Umbrils and Byrgens, which could be rather nice for a solo mage. Slightly higher level than Marjami.
A little lower than Marjami level is Cirdas, there are Umbrils and Acuexes by the Skirmish thing. SW from there is also a room filled with Worms, Funguars, and some other typical cave crap, I forget what, but it's rather unknown and could easily gather a lot of enemies (well, except worms).