Our wiki has the details of where the best places are to find the enemies you want.
http://www.disneyonlineworlds.com/index.php/Enemies
and more specifically about the huge gator:
http://www.disneyonlineworlds.com/in...Huge_Alligator
I'm also sure there are more places that listed on the wiki but can't remember.
EDIT: I've added the locations to the wiki and here they are for those not wanting to visit the wiki :P
Cutthroat Jungle (Cutthroat Island), Misty Mire (third fly trap - Tortuga), El Sudoron Jungle (Padres Del Fuego)