You have to trade a Cubone from Leaf Green or Fire Red.
pokeflute
you go to the marsh area
route 203 (mass outbreak).
Piplup does not exist in Pokemon LeafGreen or FireRed.
Seven island.
You find in the ghost building.(sorry im not specific.)
In Pokemon Tower in Lavender town
you can buy a cubone in the shop when you get enough money in the gambling place
You have to trade a Cubone from Leaf Green or Fire Red.
pokeflute
In both games you'll have to trade a Cubone from FireRed or LeafGreen.
cubone have it
Cubone can be found in the Pokemon Tower (aka Lavender Tower) in Lavender Town. There is a 5%-14% of finding a cubone depending on which floor you are on. 24 is the highest level that you will find them. In the Japanese version of Pokemon blue, cubone can only be obtained through trading.
you go to the marsh area
route 203 (mass outbreak).
Piplup does not exist in Pokemon LeafGreen or FireRed.