I know you can get the alakamite there, any others?
Nope each vary on different things such as location, time, and if you completed the game or not.
No. Only the Alakazite stone is there.
Here are the locations for all of the known Mega Stones: http://pokemondb.net/pokebase/163342/whats-the-location-of-all-mega-stones?show=163342#q163342