I've managed to do it in Pokemon Yellow and Platinum. I am not too far off from doing it in W2 (have over 500, and a lot of the ones remaining are the lower evolutions of Pokemon I transferred from SoulSilver)
When Snake sees a "!" over someone's head, he runs and hides. When the Pokemon Trainer sees a "!", he beats them up and takes their money.
I did it for Red and Silver, and now I'm trying for it in Black 2. Since the first of the year I've collected at least 3 new pokemon every day. Up to around 250 now, plus the pokemon I have in my Black and White versions. If I keep going like this, I should be ready for X and Y well before October.
GT: TwilightWolf000 PSN: SquireRamza Black 2 FC: 1206 7052 5893