I think one of the prizes for the Pokeathlon was a firestone.
*NOTE* The prizes change each day.
There are a few ways you can get it, one is to come 1st in the Bug catching contest at National Park, another way is to win the Pokeathlon, or in Kanto, you can show Bill a growlithe or a vulpix and he will give you one.
Either from the "warm beach" route on the pokewalker. By showing bill's grandfather a growlithe on request. For winning the bug-catching contest (sometimes) or bought at the pokeathlon dome on a Sunday, Tuesday or Thursday
There are five ways, one by pokeathlon - two by bug catching contest(i think) - three by getting in captured Pokemon - four by getting in the getting lost items or dropped in the routes and forest etc. and five by trade or import from GBA games.
You can find it in Pokemon Platinum, Pokemon Crystal, Pokemon HeartGold, and Pokemon SoulSilver.
Find and then catch
Cynthia is not the champion in the johto region in Pokemon heartgold,you can't find her in it, but she is the champion in Pokemon pearl,diamond, and platinum versin and that is the sinnoh region.
You can only find Skarmory in the Pokemon SoulSilver version.
I think that TM energy ball doesn't exist in heartgold. You can find it in Pokemon diamond and pearl on ds.
Buy it at KANTO Region at Department Store
somdays check the prize exchange at the pokethonal dome or bills grandpa in kanto
you can find a firestone in national park after you get enough points you can buy one
dowsing machine maybe
You can't find registeel in Pokemon HeartGold.
You can find it in Pokemon Platinum, Pokemon Crystal, Pokemon HeartGold, and Pokemon SoulSilver.
unkowns {pokemon}
You cannot find Latios in Pokemon HeartGold unless you went on wi-fi and got the Enigma Stone
There is no such thing.
You can't
yes
trade