In both games you'll have to trade a Cubone from FireRed or LeafGreen.
You have to be patient and wait until one appears - they are quite rare. Or you could catch a Cubone in the tower in Lavender Town and evolve it.
you can buy a cubone in the shop when you get enough money in the gambling place
Seven island.
In Pokemon Tower in Lavender town
in Pokemon tower btw i LOVE Pokemon
You can get Cubone by catch it in Pokemon Tower (The place fill with a lot of ghost pokemon_)
You find in the ghost building.(sorry im not specific.)
In Pokemon heart gold Cubone is found in Rock Tunnel and Safari Zone
You can not catch it in leafgreen,but in firered you can.
you cant get toros on leafgreen you need to catch one on firered and trade it to leafgreen
Cubones can be caught on Seven Island.