The weirdo next to the Pokemon center in violet city(you need shards)
inside rocks,pokewalker,trades,held items(mostly bidoofs)inside pokeballs.
Chat with our AI personalities
Regular BERRIES. (Oran Berries in HeartGold).
feed oran berries to miltank named moomoo
if you go to dept store in goldenrod city and go to the 6th floor then go the prize draw place then wait until you get an oran berry.Get them from the Man next to the Pokemon Center in Violet City and give him a few Blue Shards and he'll give you a few Oran Berries grow more Oran Berries in the Berry Pots.
after you give the miltank all the seven oran berries (its random the number of oran berries mine was 14 there diffrent oran berries you have to give it some times)they will give you the seal case.
You can't exactly buy oran berries. They are found on trees on paths and tree patches.