You can find Moonstones via the following: Reflection Cave, Terminus Cave, Secret Super Training (Drag Down Hydreigon!), Route 18 (from Psychic Inver), held by wild Clefairy and wild Lunatone. You can also randomly win one from the Balloon Popping game on the Pokemon Global Link website on Level 3. To obtain items from the Global Link website you must obtain a Game Sync ID via the PSS in-game and then use it to register on the website to sync your game card with the website. You must also use your obtained Poke Miles to play the Balloon Popping game which are obtained from StreetPass, Walking, and Interacting with people on the PSS.
In Pokemon X and Y you are not allowed to sell mega stones unfortunately. They are considered a special item.
There is no such thing as a mega stone in Pokémon Pearl. Mega stones were first introduced in Pokémon X and Y and are required for certain Pokémon to Mega Evolve, which is a temporary new evolution stage.
No, because Mega Evolution wasn't introduced until Pokemon X and Y.
Nowhere. As of now there is no such a thing as a Mega Salamence.
Aerodactyl doesn't have a traditional evolution. It does, however, have a Mega Evolution, which you can evolve it to by having it hold the Aerodactylite and selecting "Mega Evolution" during a battle.
You cannot find the Mega Stone for Latios in Pokémon X or Pokémon Y.
That's unknown. Arceus is already too strong as it is now, it doesn't need a Mega Evolution, and holding a Mega Stone would prevent the use of the Multitype plates anyway.
So far there have only been 6 named Mega Stones: Lucarionite, Blazikenite, Mewtwonite X, Mewtwonite Y, Charizardite X, and Charizardite Y. Lucarionite is the only one listed prior that can be obtained through normal gameplay in both games. Blazikenite must be obtained through an event, which begins on October 12 and lasts until January 15, 2014. Mewtwonite X and Charizardite X can be obtained only in Pokemon X, and Mewtwonite Y and Charizardite Y can only be obtained in Pokemon Y. Mega Stones can be traded between these two games.
The Mewtwonite X is exclusively for Pokémon X while the Mewtwonite Y is exclusively for Pokémon Y, so in order to get both Mega Stones (or more of the same one) and another Mewtwo in a single game, trading is required.
Charizard is the the final evolution of the line beginning with Charmander. It cannot evolve into another form (at least in the non-hacked games). It can, however, breed (at the Pokemon Daycare) and produce an egg which will give you access to an earlier evolution. Charizard can also Mega Evolve into two forms: Mega Charizard X or Y using Charizardite X or Y. Mega evolution, unlike regular evolution, is temporary, only happening during battle.
yes
He is in lots of different Pokemon games, like diamond and pearl.