There's no specific place to find one Red Gyarados like in Gold/Silver/Crystal/HeartGold/SoulSilver, although you can encounter one through the normal 1/8192 chance of encountering a shiny Pokemon. You can also transfer one from HeartGold/SoulSilver by transferring it to Black/White/Black 2/White 2, then transferring it from there to X and Y using Pokemon Bank and Poke Transporter.
there is no Pokemon x... if there is its a glitch or an action replay code
It's catchable in Red/Blue/Yellow, FireRed/LeafGreen, HeartGold/SoulSilver, and X/Y. You catch it in the Cerulean Cave in Cerulean City in Red/Blue/Yellow, FireRed/LeafGreen, and SoulSilver, and the Unknown Dungeon in the Pokemon Village in X/Y.
you can catch spinarak in route 30
Scyther is a Pokemon from the original game. In Pokemon X, you catch one on Route 21 but they are very rare.
No, you cannot catch Mew in Pokémon X.
there is no such thing as lvl X in the Pokemon games
You can catch Mewtwo at the Unknown Dungeon after beating the Elite Four and entering the Hall of Fame.
In terms of Legendaries, most of the ends of the caves in Pokemon X and Y (Like the Sea Spirit's Den in the Azure Bay near Korrina's town
Duskull maybe?
You can't catch Charizard in Diamond. You'll have to migrate or trade Charizard to get it in Diamond. You can have a Charizard in FireRed/LeafGreen and HeartGold/SoulSilver and X/Y, if you evolve Charmeleon. To get Charmeleon, you need to evolve Charmander or in X/Y you can find it at the Friend Safari. In FireRed/LeafGreen Charmander is a Starter from prof. Oak and in HeartGold/SoulSilver you can get it as reward from prof. Oak for defeating Red.
Underground Waterways (Requires Cross + Burn x 2)
You can find Meinfoo on Route 8 or in Fighting Friend Safari's.