I'm currently on the quest; 'Exotic Substances' and I've killed over 20 or more Coral Snakes and none of them drop any of their fangs. I've gotten fangs from Giant Mambas but not from Coral Snakes, any ideas?
I feel your pain. The Exotic Substances is one of the most cited quests for frustrated drop-rates. Due to the nature of drop rates, a small percentage of players will be unlucky and have to grind well past what seems fair. It's the dark side of random number drops.
There's a more detailed and nerdy discussion here, including a chart showing estimated failure rates for various situations. But here's the general idea: due to the nature of drop rates, there's an expected group of players that will struggle to get an idea to drop. It's just the why randomness works on a bell curve.
The plus side, is that there are so many random drops in the game, it's quite likely that you'll be on the lucky side for a lot of items (getting them first try, etc), as often as you're on the unlucky side.
One of the challenges facing this particular drop item is the very limited number of enemies that drop it. In theory, if the world map is expanded again to add more of the jungle, there'll be more enemies on that map that could drop the fangs. That would help a little. No idea if that is, or when, it would happen.