Trying to do the Island museum and Professor Snail says that snake spines can be found on the western side of the island but I just keep finding snake skulls. Is this a bug or is there a more specific way to find them?
The "western farm" area is where you can find them, yes. Any and every chance you get, dig at artifact spots there and you'll eventually find them. You need two. As far as I can tell, too, this is the only way to find them.