Pidgey can be found in several areas and can often be found on Route 1.
You can migrate one from Firered or Leafgreen.
You can get Pidgey by migrating from FireRed/LeafGreen or by trading with Platinum.
Pidgey cannot be caught on Pokémon Sapphire, so you will have to trade it from someone who has it or from FireRed/LeafGreen.
You must have a Pokemon firered or leafgreen trade you a pidgey then train it to level 36 and it will become a pigeot.
No one in the game trades you rattata nor pidgey if you want to trade those Pokemon use a link cable or wireless adapter to trade with leafgreen or another firered.
It elvolves from Pidgey at level 18 and evolves into Pidgeot at level 36.
Pidgey -> Pidgeotto -> Pidgeot 18lv. 36lv. If you don't understand, then the evolution is: Pidgey will evolve in 18lv. to Pidgeotto and Pidgeotto will evolve in 36lv to Pidgeot.
caterpie, metapod, weedle, kakuna, pidgey, pikachu, and i think pidgeotto might be in leaf green, but it is in Pokemon yellow
start game with charmender .catch a pidgey,pikachu,nidoran♀,geodude. raise this pokemons and after you have raise enough you should try to catch legendary Pokemon
you cant find a pidgey in Pokemon emerald the only way to get a pidgey is to trade with Fire Red or Leaf Green
find a friend with leafgreen who needs a rattata.
Pidgey evolves at level 18.