Outside of Japan you're going to have a hard time. You can find people selling bundles of cards on yahoo Japan frequently fairly cheap, but unless you live there you'll have to use a proxy service to bid on them which will rack up the price and sooner or later you'll hit that sweet spot where it's not viable to buy them in lots anymore because you'll get more doubles than new ones. On occassion you'll find a box of unopened booster packs as well, though those tend to go fairly high in price.
You'll also need to find a Starter Set as the cards in that are unique and can't be found in Booster packs.
There's also 556 cards in total for Chapter 1 spanning Suikoden I - III and 790 cards for Chapter 2 spanning Suikoden I - IV, and Chapter 1 cards are much more common as Chapter 2 is pretty much what killed the game. Total numbers don't take into account the "special" cards with printed signatures of the artist on them either.
All that said, if you have a decent number of doubles that you're willing to trade I might be interested.
Doctorum Non Urina Singulus.