Audino can be found in almost anywhere in the game. Go to a route and find a patch of rustling grass. You can hear the sound effect to determine whether a patch of rustling grass is present.
Rustling grass appears by luck. Just use a repel or avoid the grass and stay on the route and walk or cycle around until one appears.
Audino is very common in rustling grass. You can find it easily, or maybe some rare Pokemon like Gliscor.