Serebii.net says that you can get Spiritomb in B2/W2 by trading with Ruri or Tetsu (who are they, anyway?) but doesn't give any further details. Can anyone elaborate on how to meet this person and trade with them? Thanks. --- This game will blow your mind...out of your nose. - ad for Psychonauts
See http://www.serebii.net/black2white2/forgottenitem.shtml for more details.
In the English versions, they're named "Yancy" and "Curtis." Whichever of the two you'll encounter depends upon the gender of your character (male: Yancy, female: Curtis). --- Currently ignoring: Real Life