I suppose there's a few fish species that thrive in both fresh and salt water that can be used and do live in the Philippines (Terapon jarbua, archerfish, maybe a few gobies?). Other than that I think your best bet for a small island nearby with a lot of fish life would be Sulawesi, which has various small ricefish and the Celebes rainbow, which could probably be held with snakes and sailfin lizards just fine.
For the warty pigs and crocodiles you might want to look for the more widespread and larger species from Sumatra, Borneo, etc. But I really don't have enough knowledge on USA holdings to give you examples