Question

When do I get the Blue Orb from Mr. Pokemon (in HeartGold)?

Answer 1

>From Mr. Pokémon after both the National Pokédex and a Kanto starter Pokémon has been obtained from Professor Oak

You need to get the National Pokedex from Professor Oak and beat Red at Mt. Silver so you can get one of the Kanto starters from Professor Oak, then talk to Mr. Pokemon.

Source