Well, Snivy isn't in the game at all, so you're going to have no luck with that. At least until the pokebank comes out, in which case if you have one in your Gen V games you can transfer it over to X and Y. Gothorita, on the other hand, can be found in Psychic Friend Safaris. If you want a Gothita, then you can breed it for one.
The only ways that I am aware of to currently get hidden abilities in X and Y is through the Friend Safari and through Horde Battles. You can also obviously get them through breeding, but you already need to have a Pokemon with a hidden ability for that.