Blue shard
If you already have the berry pots and some sense of time you can grow them really easy. If not the best place is to use the Pokewalker to get shards and trade with the juggler in violet city next to the Pokemon center
You can get it two ways: #1: Go to the juggler in Violet city and the #10 offer is some shard for a sitrus berry and 2 other berries. #2: Go to the juggler in Fuchsia city and the #10 offer is some shard for a sitrus berry and 2 other berries So the only difference between the two choices is location...
Violet City - the juggler next to the Poke Center
In Violet City, give the Juggler a Yellow Shard and he'll give you the Yellow Set, which has the Sitrus Berry in it. Also you can go to Ruins of Alph to get it.
West of Violet city.
you have to beat the elder at violet city
You go north from cherrygrove city.
In violet town behind the pokémart
on the far left in the city
if its on pokemon soul silver, just use your super rod in violet city.
You don't trade the shards for stones, you trade them for berries. You trade them with the man standing outside the Pokemon Centre in Violet City, and you'll get 3 berries from a specific set depending on the colour of your shard
It is given to Mr. Pokémon near Violet City for experience.