Talk to a Saab mechanic. A Saab-certified mechanic in your area can tell you where to buy the best parts. Most Saab dealerships have parts departments that stock genuine Saab parts. Saab parts are more expensive than after-market parts. You'll have to know whether the part you need has to come from Saab.
Consult a Saab club. Saab enthusiasts are a welcoming band of do-it-yourselfers. Contact a local club or make contact online. You can probably find someone who has bought the part you're looking for and can point you in the right direction.
Know your part numbers. If you are going to shop for after market parts, you need to know exactly what part you are looking for. If you don't have a name and a part number, talk to a mechanic. Or consult a mechanic's reference for your particular year and model Saab.
Compare prices. Beware of buying the cheapest parts you can find. This may work for Chevys, but a Saab is a different breed. Ask any Saab mechanic: genuine Saab parts are the only truly reliable ones to use. If price is an issue, try to find used parts, but be sure you get the real thing.