You need to beat Pokemon Ranger 1 or 2, then complete the mission to retrieve the Manaphy egg. Then you transfer it to Pokemon DPPt.
Or, in Pokemon Platinum, you can see Manaphy's picture in a book in Mr. Backlot's mansion and then get it on the GTS.
You'll Have To Catch It With A Pokeball.
To receive a Manaphy in Pokemon Platinum, you must send over a Manaphy Egg from the game Pokemon Ranger after completing a special mission involving Manaphy.
you don't get them together you have to find the sea crown and get manaphy from Pokemon ranger
you have to catch a dragon Pokemon holding a dragon scale
you get the manaphy egg in Pokemon rangers and send it into Pokemon diamond or pearl
You can not find or get manaphy on Pokemon diamond but you can by hacking, trading or... if you have Pokemon ranger you have to complete the manaphy mission and then you can put it onto diamond.
To get a Manaphy in Pokemon Diamond you have to get Pokemon ranger and defeat it and you have to trade it to Pokemon Diamond,Platinum or Pearl.
There is no trainer in Pokemon Platinum with a Manaphy. However, you can trade with someone who has a Manaphy, or complete the special Ranger mission in Pokemon Ranger and transfer the Manaphy egg over to Pokemon Diamond, Pearl, or Platinum.
you go to feugo iron works and use poke'radar.
info on manaphy in Pokemon mansion. trade for manaphy, and breed with ditto. you get a phione
you find a egg in the surronded sea and the next day it hatchs into manaphy
you find it on map land 8.