NIntendo wants to help Pokémon trainers collect some of the rarest pocket monsters. The publisher is working with GameStop to offer the “Shiny” versions of three legendary Pokémon. Shiny Pokémon are hard-to-find versions of characters with alternative colors that some fans highly covet.

For those gamers, Nintendo has a new promotion that will have GameStop stores around the country offering three Shiny Pokémon for previous games in the franchise.

Starting on Aug. 19, Nintendo will begin distributing the shiny version of Steel- and Dragon-type pocket monster Dialga. Trainers will have three weeks to capture Dialga. Following that, on Sept. 9, GameStop will offer a Shiny version of Water- and Dragon-type Palkia for another three weeks. Finally, from Sept. 30 until Oct. 20, Pokémon fans can grab Ghost- and Dragon-type Shiny Giratina.

To get these Legendary Pokémon, gamers will have to bring in their 3DS or DS consoles with a copy of Pokémon Black, Pokémon White, Pokémon Black 2, or Pokémon White 2 to any GameStop location. Gamers can catch Shiny Pokémon in the games without special events like this, but it typically requires hundreds of hours of play to naturally find these rare-color Pokémon.

Pokémon X and Y for 3DS will hit retail and Nintendo’s eShop Oct. 12.