To get Ball Capsules, the Seal Case is required. Go to Sunyshore City and go up until you see a building that has ribbons on it. Enter it and walk up to find a man with glasses that lets you buy Ball Capsules. Buy one, go to the Pokemon Center, then go to the PC. Go on your file, go to Ball Capsules, and select a Pokeball. When you see an icon, use your stylus and drag the icon to the Pokeball. Put on as many as desired. Select "Confirm" to make a Ball Capsule.