On Pokemon LeafGreen how to get ultra balls?

you can get ultra balls in a store after you beaten 4 gym leaders

Different person edit - no, you can't actually. I'm playing the game right now, and I've beaten 6 gyms, and I still can't get ultra balls. So there. ;P anyway, I believe the first time you can get ultra balls is on Cinnebar island. I think.
you buy them in a pokemart in cinnabar island for 1200 dollars a ball