I think what you had there about Pidgey is pretty neat, it's cool to think about.... But anyways;
THERE ARE TWO WAYS TO GET MISSINGNO IN POKEMON BLUE!!!
The first way is the most popular. You talk to the old man that teaches you how to catch a Pokemon, then you fly to Cinnabar Island. You then surf up and down the west coast to find Missingno.
BUT I FOUND ANOTHER WAY TO FIND MISSINGNO!!! You can find him as soon as Lavender town, as long as you have a Pokemon that can learnTeleport. So first, you walk west of Lavender Town, and keep walking all the way west until you see the man looking straight up at the door. Walk in his line of sight, but one block above where he appears on you're screen. Basically, you'll be standing right in front of the door. Then walk down and immediately press start. Use teleport, you should fly away just after he "see"s you. Now go down towards where all the fishermen are, and go through the gate. Fight the SECOND fisherman you see, and make sure he has to walk up to you to battle you. His first Pokemon will be a Tentacool. After you beat him, teleport back to Lavender town. I don't know if this part is required, but I went to the Pokemon Center and used the PC first. Then, walk west again towards the route where we walked all the way west. Your menu should pop up. Close the menu, and you'll be engaged in battle. It's a level 7 Missingno!