There isn't a third floor in Pokemon Yellow. There's not even a second floor unless you count the trading/battle coliseum. And for that you need to find another player, wire up, and do it that way.
beat team rocket.>:(
On the top floor of any Pokemon center.
You can trade from firered version on second floor of the Pokemon center after you get the pokedex.
What you do is, you got to any Pokemon center. Got to the second floor and trade with a friend that has it in diamond, pearl, or platinum.
In Nimbasa city,top left building of Pokemon center in the 1st floor,a boy sitting on a chair gives it to you
It's on the second floor of any Pokemon Center.
On the top floor of the Pokemon center.
second floor in the seafoam islands
Walk up the stairs.
it's on the second floor in the Pokemon center CHEESE!!!
Go to the bottom floor of the Pokemon center
in a Pokemon center 2nd floor
lost tower 5th floor