In Diamond/Pearl: Trade for TM18 (<a href="http://pldh.net/dex/move/raindance" class="linksred">Rain Dance</a>).<br />
In Platinum: Trade in exchange for move tutoring. Visit <a href="http://pldh.net/guides/dpp/shardsandtutors" class="linksred">here</a> for more.<br />
In HGSS: Trade in exchange for a variety of berries. Visit <a href="http://pldh.net/guides/heartgoldsoulsilver/shardsandberries" class="linksred">here</a> for more.