You can not get two xp shares in Pokémon Diamond (that I know of).
You can trade exp shares from other Pokémon games to your Pokémon Diamond Version. That is what I did.
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Nope
You can get the two Exp. Shares in Pokemon Black and White these ways:1.) Go to Iccirus City. Go into the Pokemon Fan Club and show your starter Pokemon to the guy in the middle of the room. If your friendship is high, he'll give you an Exp. Share.2.) Go to Castelia City. Enter the Battle Insitute. Battle and beat everyone, and on the highest floor, if you beat everyone, you can beat the director and he'll give you an Exp. Share.
You can either get it in the game, which apprently you CAN in pokemon black and white. And just as the previous contributor said, You can trade with your friend and then BAM! You get an experience share!
You can find a moonstone in Devon Corp the Prezident will give u 1 but he shuld give u an exp share 2
You can find it in the Great Marsh with dual slot Firered. Dual slot means you put diamond in slot 1 and Firered in slot 2.