What Pokemon Obtainable in Black 2 Evolve Through Trading?

Question

Could Hold A Item To Evolve

Answer 1

Seadra > Kingdra (holding a Dragon Scale)
Onix > Steelix (holding a Metal Coat)
Magmar > Magmortar (holding a Magmarizer)
Feebas > Milotic (holding a Prism Scale)
Clamperl > Gorebyss/Huntail (holding a Deepseascale or Deepseatooth)
Boldore > Gigalith
Karrablast > Escavalier (trade with Shelmet)
Shelmet > Accelgor (trade with Karrablast)
Slowpoke > Slowking (holding a Kings Rock)
Poliwhirl > Politoed (holding a Kings Rock)
Gurrdurr > Conkelldur

These are all of the Pokémon I could find. Hope I helped!

Sources: Trade evos and Unobtainable Pokémon

Answer 2

Since you specifically state "Black 2" this does not include the Pokemon that are exclusive to White 2 (Electabuzz is the only one that fits this). Also it does not include Pokemon found in the post-game. This is because in the post-game you have the National Dex, and so can theoretically get any Pokemon at all.

• Magmar: Evolves into Magmortar when traded holding the Magmarizer.
• Boldore: Evolves into Gigalith when traded.
• Onix: Evolves into Steelix when traded holding the Metal Coat.
• Gurdurr: Evolves into Conkeldurr when traded.
• Karrablast: Evolves into Escavalier when traded with Shelmet.
• Shelmet: Evolves into Accelgor when traded with Karrablast.

As far as I can tell, that is it.