In HG/SS you trade Shards for Berries. Trade with Jugglers in Violet City and Fuchsia City.
The color shards you can find in Pokemon Platinum are Red, Blue, Green, and Yellow Shards.
You can get them using the dowsing MCHN on the Pokewalker or you have a chance of getting them by using Rock Smash on any rock (You can get red, blue, green and yellow shards this way as well as heart scales, revives, max ethers, and fossils).
You cannot buy but you can teach your pokemon new moves in exchange of shards.
There is no best Pokemon on Pokemon HeartGold.
The pokewalker and the ruins of alph.
In HG/SS you trade Shards for Berries. Trade with Jugglers in Violet City and Fuchsia City.
you can trade them with the guy in front of the Pokemon center in violet city and he gives you 3 different berries for each shard
Yes there are shards in Pokemon diamond
Shards are different stons.
The color shards you can find in Pokemon Platinum are Red, Blue, Green, and Yellow Shards.
They can't be bought. You can find them underwater, or attached to wild pokemon. Chinchou have yellow shards, Clamperl have blue shards, Relicanth have green shards and Corsola have red shards.
Catch Clamperl, Chinchou and Relicanth most of these Pokemon hold shards
You can get them using the dowsing MCHN on the Pokewalker or you have a chance of getting them by using Rock Smash on any rock (You can get red, blue, green and yellow shards this way as well as heart scales, revives, max ethers, and fossils).
There is no underground because you are in a different region. Only Sinnoh region has the underground, You have to find shards and heart scales in rocks. To do that you have to use rock smash.
You cannot buy but you can teach your pokemon new moves in exchange of shards.
There is no best Pokemon on Pokemon HeartGold.