* Goldenrod City: This city has a variety of shops, including a Department Store, a Game Corner, a Pokémon Center, and several other stores selling items like Poké Balls, potions, and TMs.
* Ecruteak City: You can find the "Poké Mart" which is the standard shop for purchasing essential items like Poké Balls, potions, and other consumables.
* Other Towns and Cities: Every town and city in HeartGold typically has at least one "Poké Mart" that sells the basic items.
So, while there isn't a single, dedicated "shopping center," you can find all the items you need by visiting the various shops in different towns and cities.