If you check Serebii's archives for that date, he posted it there too.
HG/SS was announced on May 8, 2009: http://www.pokemon.co.jp/info/game/g090508_01.html but unfortunately the link is inactive too. You can go to archive.org and paste the link in there though, then click any of the dates and it will take you to what the page was. You can do the same with the Gen V announcement too: http://www.pokemon.co.jp/info/game/g100129_02.html.
Hey, can you get me links? Like I said, I wasn't active during that early period with the site so minor details aren't in my memory. Earliest revealings I remember are Zorua/Zoroark which was when I started paying attention to this site/game news updates.