I did not say catch, I said see.
It is impossible to get a "seen" Pokédex entry for Rufflet and Skitty in Black 2 as well as Vullaby and Buneary in White 2 without trading with another player, because they cannot be found in the wild in the respective games, and no in-game Trainers use them. However, each of their evolved forms are used by several Trainers in-game in both versions. It is also impossible to get a "seen" entry for first and third stage of the starter weak to player's choice as there are no in-game Trainers who use them. The second stage, however, is used by Nate/Rosa at Nimbasa City against the Subway Bosses. If the player has used Memory Link, a "seen" entry will be gotten for the third stage of said starter if Cheren or Bianca had it as one of the player's rivals in Black and White.
source
