Personally I'd rather buy these packs as an investment and keep them sealed. POP 5 packs are starting to become increasingly difficult to find, and their value will only increase over the years. But that's me.
First of all, your best chance at getting yourself some POP 5 packs is probably from Ebay. I can almost guarantee you that these packs vanished from regular online stores years ago, because of how popular they are.
Secondly, if you're going to buy these packs (which are rather expensive), please keep in mind that:
- Even though buying old, elusive packs seems tempting because of a few good cards, please remember that you're most likely not going to get them. I'm stupid, so I regularly waste tons of money on packs from old sets. From my experience you're guaranteed to loose a big portion of the money you spent 9/10 times. I open old packs because I think it's fun, but I never rely on pulling the most expensive cards in the set to earn my money back, because you most likely aren't going to.
Simply put, the chances of pulling an Umbreon or Espeon from a POP 5 pack (currently at 30$ a piece) are slim. As mentioned above, the chance of pulling one of these cards are something along the lines of 1/40 packs, which realistically means that you'll have to buy packs for around 1200$ to pull one of the star cards.
I recommend you buy the cards you wants as singles. Unless you have an unlimited amount of funds to spend, don't rely on pure luck.