I would suggest visiting a hobby shop and buying packs there, or buying those promotional boxes like the Mewtwo one and the various tins if you want to "guarantee" a foil rare card.
It's just a run of poor luck on boosters, most likely, but The Pokemon Company, Inc. tends to distribute packs so that packs sold at hobby shops have a higher special rare rate than at big box retailers like Wal-Mart or Target. This is so they can help keep these businesses in business, as these places often host official Pokemon Leagues and official Play!Pokemon tournaments. So, as I said above, try boosters from a hobby shop.
I've had horrid stretches of luck, myself, getting the same rare 4 times in 10 straight boosters of HeartGold SoulSilver. That rare happened to be Sandslash, and Sunflora was another one I kept getting. I actually have 8 each of both of those, if my memory serves.
Basically, either keep trying the boosters or seek them out individually online or in trades.