Must have a Milotic!!!
Any blue berry will work. If you want a list, here's one.
Chesto Berry Oran Berry Wiki Berry Bluk Berry Kelpsy Berry Cornn Berry Pamtre Berry Belue Berry Passho Berry Yache Berry Coba Berry Ganlon Berry Apicot Berry Rowap Berry
The ones at the bottom have a higher chance to get a Pokéblock + Source: http://www.serebii.net/omegarubyalphasapphire/pokeblock.shtml