Cosplay Pikachu is given to you after you complete your first contest.
You need to make your own Pokeblocks. You get the Pokeblock Kit in Slateport City as you're about to leave it, after you've defeated the Magma or Aqua grunts at the museum and handed over the Devon parts to Stern. You then get lead off by the game to the contest centre and get given a contest pass & Pokeblock kit from Lisia.
To create Pokeblocks, go to your kit and select 4 berries & put them into a blender. Afterwards, you get 4 blocks of one flavour based on the berries you put in.
Serebii - Pokeblocks