How Do You Get VS Seeker in "Pokemon Emerald"?

The Versus Seeker is an item in certain Pokémon games that allows the player to re-battle opponents that he has already defeated. It is not obtainable in Pokémon Emerald because it does not appear in the game; however, there is a way to re-battle trainers in the game. The player can call trainers that they've defeated on the Pokénav and they will challenge the player to have a rematch.