Research aviation publications. Many publications cater to the airline industry and those looking to buy an airplane. These magazines will often list photos, pricing and contact information on how to reach the seller. Often times, the planes are represented by a broker, who will collect a fee for engineering the deal.
Talk to airplane dealers. They will have the latest listings and will have contacts for sellers all over the country and perhaps the world. Dealers have an inside track to used aircraft that others may not know about. In some cases, dealers work with clients who do not publicly list their aircraft, as they want to deal with serious buyers only.
Browse online listings. Avoid scams by working with a legitimate online dealer. Look for a banner indicating that the dealer belongs to a local Chamber of Commerce office or the Better Business Bureau. Call the local agencies to verify their membership. Online dealers can offer varying deals and discounts others may not.
Shop at a government auction. Many planes have been seized in drug raids, IRS liens and other means the government has. These are sold at auction for a mere fraction of the price it would cost elsewhere, as the government is looking to make the money so they do not have to keep the item in storage. You can check your paper or the government auction website to see when the next auction near you will take place.