There is no specific place that you need to look for Snorunt, as long as you are in the Icy room in the Shoal Cave. It can take a little while to find them though, they aren't the most common Pokémon around.
I found one just when I entered, three steps down and... tada, "wild Snorunt appeared, what will Espeon do?"
I think it isn't that common in the cave. Because after the first one I saw, only one after that appeared after 20 minutes.