Piximon spawns on the screen where Coelamon drops you off, that is, two screens east of the Digimon Bridge screen. Piximon spawns randomly. From my experience, the most efficient method of spawning Piximon is to continuously enter from the screen north of his spawn screen, with the toilet. What I mean is, this saves the most time. As soon as you enter you can see whether Piximon has spawned or not. He spawns, basically, in the middle of the screen, next to a banana tree. Remember, you cannot run from this battle as this digimon can be recruited.