The leichi berry raises the attack stat if held by a Pokemon (that what it says in heartgold but I am not sure if it's the same in emerald)
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the enigma berry is impossible, the leichi berry can be obtained at mirage island or from Pokemon colosseum or Pokemon xd gale of darkness, the other berries may be able to be obtained from emerald.
http://www.psypokes.com/rs/berrystats.php
Mulch
You have to wait for it to grow.
You have to ask a man in pacificlog town and ask if he can see mirage island. If he does sail east till there is an island. On top of it and beside there are the lechi berries. But I bet you'll never see the mirage island!!! It appears only when the ID number correctly, the same ID as the mirage island.