Where is the first moon stone you can get in HeartGold?

You can't get a Moon Stone in HeartGold. HeartGold and SoulSilver only have the following evolution stones:

* Fire Stone: Found in the Ruins of Alph

* Thunder Stone: Found in the Ruins of Alph

* Water Stone: Found in the Ruins of Alph

* Leaf Stone: Found in the Ilex Forest

* Sun Stone: Found in the Goldenrod Department Store

* Shiny Stone: Found in the Goldenrod Department Store

* Dusk Stone: Found in the Goldenrod Department Store

* Dawn Stone: Found in the Goldenrod Department Store

You need to trade for a Moon Stone or find it in a different generation of the game.