After you get the national dex talk to your friends sister in his house in Sandgem Town she'll say there is an outburst of pokemon(other kanto, johto, and hoenn pokemon are in the sinnoh region). So come back there the next day and she'll say, "What did the news say today, oh yeah there is a whole lot of ---------- on route ---------- you should go check it out!" So listen to her she wants you to be better the her sister/brother.