No.
You can get one from the Global Trade Center,from the PalPark, or find a wild one.
To get one from the PalPark,you will need a Gameboy Advanced game with a Swampert in it,and trade it over.If you finish your Pokedex,you can then go to the PalPark and catch it.
To find one in the wild,you will also need to finish your Pokedex.When you get your national pokedex,you will be able to encounter more pokemon.
Bertha has it beat her 5 times in the Pokemon elite 4
swampert, groudon, blastoise, glalie, latios, and feraligator
-mongmong908
No, you do not have to beat the Elite 4 to get the National Dex in Pokémon Diamond.
After you beat the elite four.
Beat Cynthia after Elite Four
Beat all the elite four and there champion
catch legendary Pokemon like giratina and heatran
finish the nation pokedex
beat the elite four and shes the champion
you have to beat the elite 4
beat the elite 4 dips hit