1. Use the Pokémon bank. This will require two Nintendo DS or DS Lite systems and a second copy of the game, Pokémon Ruby, Sapphire, or Emerald. Once you set up the migration, you can transfer a swampert to your game. If you do not have two Nintendo DS systems, you can ask a friend to help you with this process
2. Trade. Ask a friend who has Pokémon Ruby, Sapphire, or emerald, to trade a swampert with you.
3. Use the Grand Underground In Pokémon Diamond, Pearl, and platinum you can travel to the grand Underground where you can encounter Pokemon from various other regions. Here, you can eventually encounter a swampert and attempt to catch it.