You can find the spawn @ 37200, 59800.
The Spawn is time-based (if you go to the area, you will see what time the next "round" will start). The mobs comes in 12 "waves", with lower maturity mobs at the lower lvl-waves, and ending with the Boss @ wave 12.
Preferably you do join the whole "event", since it can time out on the waves if all mobs are not killed fast enough, but one is able to jump in at anytime, even only on boss. Some ppl do just that, and let the others do the hard work.