Travel the Sinnoh region and collect them. The other way to get some plates is digging underground.
In the underground, they'll appear all of them, randomly.
you dig them up in the under ground mine
i do not think there is a code try codejunkies.com if it is not there i do not know where to find it...
Find all plates and got to spear pillar................. TRICKED YOU....you need the Azure flute or action replay.
spell you trash 'platnium'=Platinum
this is the same as Pokemon platinum, they are in the underground, they do take a while to find.
buy the Pokemon platinum book
open your bag,go to key items and you will have the 'explorer kit'.With this key item you can dig and go underground.There you can dig the walls and find many treasures.If you are lucky,you will start finding plates.Then,search over and over and in 1 week you will have all plates for arceus!
you find them in the cave
you can find them in gartinas cave
a game with all the cheats you can find
It is a combination of iridium plated with Beryllium, Platinum and Gold. Its is very rare to find and only few plates were made in this way.