Hey Shawtay <3
The best place to do only killer caiman bestiary is a cave located in the zao steppe, south of the muggy plains. It's accessible after doing the first mission of The New Frontier Quest.
This is the location:
There are two floors in this cave: I was hunting in the whole cave on my EK to do tasks + bestiary once she was level 80 and the cave is really good to complete Killer Caimans.
Alternatively Killer Caiman bestiary can also be done together with High Class Lizards in the Muggy Plains, behind the Dragonblaze Peaks of Zao. That can be annoying (must not) because killer caimans are weak to fire and high class lizards are weak to ice but in that case one can also use thunderstorm runes ^^
The difference to rapid respawn events is in particular, that Killer Caimans spawn much faster, also in the above mentioned cave. It's considered as any other hunting place, since killer caimans are not categorised into "bosses" such as undead cavebear etc.