No, you can't buy berries in Pokémon Diamond.
http://www.psypokes.com/rs/berrystats.php
Mulch
You have to wait for it to grow.
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)
No, you can't buy berries in Pokémon Diamond.
In emerald you get them in the contest hall by making them with berries.
http://www.psypokes.com/rs/berrystats.php
Mulch
You have to wait for it to grow.
you can buy Pokemon emerald, ruby, sapphire, firered and leafgreen at gamestop
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)
Feed them good pokeblocks from durin berries.
you buy it
you buy it
You can buy it at Gamestop.
Pataya berries must be obtained from either Pokemon colosseum or Pokemon xd gale of darkness trade a Pokemon holding the berry to emerald then plant it to get more.