How do you get a darkball in Pokemon HeartGold?

You can't get a Dark Ball in Pokemon HeartGold. It was introduced in Pokemon Black and White.

However, you can get some other useful Poke Balls in HeartGold:

* Ultra Balls: You can purchase these from the Game Corner in Celadon City after winning enough tokens from the slot machines.

* Premier Balls: You can purchase these from the Game Corner in Celadon City after winning enough tokens from the slot machines.

* Luxury Balls: You can purchase these from the Game Corner in Celadon City after winning enough tokens from the slot machines.

* Quick Balls: These are available from the department store in Goldenrod City after you have beaten the Gym Leader there.

* Net Balls: These can be purchased from the department store in Goldenrod City after you have beaten the Gym Leader there.

* Dive Balls: These can be purchased from the department store in Goldenrod City after you have beaten the Gym Leader there.

You can also find Great Balls in various locations throughout the game, and Poke Balls are available for purchase from many shops.