OK, I restarted Yellow, and I'm in the Viridian Forest. But I can't find any @$#%ing Pidgeotto! I KNOW they appear in this forest in Yellow, but WHY haven't I found one yet?! Anyone know the exact appearance rate of Pidgeotto here? And NO, I will NOT settle for Pidgey.
Their pretty rare, so keep looking, sooner or later you will run into one. While you're looking, either battle the pokemon that show up and is not Pidgeotto (if you pokemon need levels) or run away if the pokemon shows up is not Pidgeotto (if they don't).