The following heartless drop the dark shard:
Shadow (all worlds)
Soldier (all worlds)
As far as i know, none of the nobodies drop it
Dense Shards are found in Twilight Town, Hollow Bastion, The World That Never Was, and Beasts Castle
I don't think you can find Mythril Shards in Heartless. Only in Treasure Chests around other worlds.
Kingdom Hearts- Air Pirate, Battleship, Pirate Kingdom Hearts II- Aerial Knocker, Shaman.
Power Crystals can be found by defeating Wyverns in Kingdom Hearts and Morning Star in Kingdom Hearts II.
Some are random and some are in treasure chests, things like lightning shards, twilight shards, dense shards and those kinds of things are found from heartlesses and nobodies. But things like Orichalcums you find from treasure chests, and some you can get from the heartless that looks like a candy machine
You find all your answers for Kingdom Hearts on "wiki Kingdom Hearts"
There are no Gameshark codes for Kingdom Hearts 2.
Hot Topic, You can go on-line at hottopic.com and search kingdom hearts and there's a kingdom hearts necklaces and other things.
You have to earn them.
There is no possible way of finding Xemnas in kingdom hearts. You are only able of finding him in kingdom hearts 2, which he is the last boss in the game.
You can find Kingdom Hearts in: * Gamestop * Wal-Mart * Best Buy Hope this helps! =)
Kingdom Hearts backpacks, shirts, and other accessories are available at Hot Topic.