Teak is plenty strong, but what do you mean by tribal spear? Most primitive fish spears were launched from above the surface.
I used to sell stingray bycatch from bay shrimping to a neural research lab.We always removed the barb for safe handling. I don't think they would make a very good tip. They're not flat, have a bit of a curve. They're serratted, and not real sharp or strong. I'd try honey locust thorn for small fish or bone for something larger. Ben Hunt's old books show trident designs with a long central icepick flanked by 2 flexible curved tines to hold the fish .You might try fire-hardening a tip from dogwood or osage orange, either of which make good shafts.You could also make a slip tip toggled point from antler. Heat it in water then straighten it out I and shape it.
I don't know of any primitive elastics, but you can gig flatties with direct muscle power. Good Luck!