Can I acquire the generation I starter Pokemon in White 2 / Black 2?

No. Pikachu, Squirtle, Charmander and Bulbasaur can only be obtained in Black/White 2 by trade, or special events.

Ways to obtain Pikachu and the Red/Blue starters in BW2 include:

• Time-limited Wi-Fi, Global Link and Dream World events: keep an eye on Bulbanews' events listing. For example, you can currently download the Red/Blue starters if you have a Korean copy of Black/White, or Pikachu if you buy the game on Amazon UK. At time of writing, there are no English language events for these Pokémon.
• Find someone online who will trade you one - quite easy, since Pokémon can be bred. You can't use the GTS for this, though, because you can't request a Pokémon you haven't seen
• Trade from an earlier game using Poké Transfer:
  • Professor Oak gives you a Bulbasaur, Charmander or Squirtle in HeartGold or SoulSilver when you defeat Red
  • You get a Bulbasaur, Charmander or Squirtle as a starter in FireRed and LeafGreen
  • Pikachu can be caught in every main series Pokémon game on the GBA and DS, prior to Black/White

Interestingly, Black and White are the first main series Pokémon games where you can't catch Pikachu - except for Yellow, technically, where you receive one as a starter.

You can acquire them only via Poké Transfer.