The Jirachi pokemon cannot be caught or obtained by any normal means in Pokemon Emerald. It can only be downloaded from a bonus disk, the Pokemon Channel or — previously — an event sponsored by Nintendo.
The bonus disk is given along with a pre-ordered Pokemon Colosseum USA Disk (NTSC). This disk allows the player to transfer a Jirachi to Pokemon game versions Ruby and Sapphire after the player has unlocked the trade feature in the games. Once the Jirachi has been transferred to either Pokemon game versions, the player can then transfer it to Pokemon Emerald.
For those who are in Europe, the Pokemon Channel (PAL) gives the player the option of transferring a Jirachi to Pokemon Ruby and Sapphire versions, then it can be transferred to Emerald afterwards. Originally, Jirachi could only be downloaded from a Nintendo sponsored event with one one taking place in 2010. The Jirachi pokemon was given out at Gamestop stores from February to March during that year.