There isn't a Space Center in Pokemon Diamond and Pearl.
Go to a Pokemon center to make space for the egg then go back and they will still be there.
You go to a Pokemon center.
Pokemon Diamond? If so yes there is.
Get a Graveler and trade it in any Pokemon center
in platinum she is in the Pokemon contest center
In Hearthome, next to the Pokemon Center.
North and west of the Pokemon center!
you dont
the trade center is up stairs in the poke center
There is no space center, that is in ruby, sapphire and emerald.
heartthrome city house next to the Pokemon center
upstairs in the Pokemon center first door