How to obtain.
Interested in having a Gardevoir of your very own? Then you've come to the right place! Though Gardevoir itself cannot be found in the wild, its previous forms––Ralts and Kirlia––can. So here is a list of where you can find them in the wild. Because Gardevoir does not appear in any Pokémon games prior to Pokémon Ruby/Sapphire this list will only cover locations from generation III to present.
Ruby/Sapphire/Emerald: Can be found on Route 102.
FireRed/LeafGreen: Trade from Ruby/Sapphire/Emerald.
Colosseum: Trade from Ruby/Sapphire/Emerald.
XD: Can be found in Pyrite Town as a Shadow Pokémon.
Diamond/Pearl: Can be found on Routes 203 and 204 using the Poké Radar.
Platinum: Can be found on Routes 208, 209 and 212.
HeartGold/SoulSilver: Can be found on Route 34 during a swarm.
Black/White: Can be found in White Forest (Pokémon White only).
Black 2/White 2: Trade with a trainer in Nimbasa City.
X/Y: Can be found on Route 4. Can also trade with Diantha in Lumiose City after becoming the Champion.
Omega Ruby/Aplpha Sapphire: Can be found on Route 102.