Shop around when looking for restoration parts. There are numerous sources for new and used parts, including online parts catalogs, auction sites and local classifieds. When buying used, deal locally whenever possible so you can thoroughly inspect the part.
Shipping costs are a primary consideration when buying auto parts, especially large items such as body panels or engines. It may be cheaper to buy a part locally and repaint or rebuild it than to have a pristine one shipped, especially if you do the work yourself. Shipping cost is based more on box size than weight, so If you must have something large shipped, plan ahead and buy multiple items from the same seller to get the most for your money.
A good place to find parts is the classified section of various car enthusiast forums. Many forums have some sort of vetting system, so you can be sure you're dealing with an honest seller. It is also easier to get extra pictures of parts.
If you need a lot of parts, consider buying a second truck that complements yours, and scavenge parts from it. For example, if your truck has a clean body but a damaged engine, buy a truck that was rear-ended, and use its engine. Sellers of trucks like these typically just want them gone and let them go at good prices. You also have the option of selling unneeded parts to make some money back.