Pokémon Gaming CentralFor topics that aren't necessarily restricted to one game, Pokémon Gaming Central ranges from comparing and contrasting the differences in the gaming generations to discussing the gaming franchise as a whole.
Without knowing what game this is for, I can't accurately tell you what to do or where to train. I'll lock this for now, since you have decent answers, but if you need more specific information, try asking in the correct Q&A thread. For example, if this is for Black 2, ask in the Black and White 2 forum's Q&A thread. :)