Instructions
Search through the listings on eBay, which often has a wide selection of pre-built and unassembled plastic model trucks.
Search through the "for sale" section in online classifieds, such as Craigslist and Kijiji. If you cannot find plastic model trucks for sale, you can post an ad stating what you are looking for. Many online classifieds allow you to post a basic ad for free, or a premium ad for a specified price.
Search for plastic model trucks online. Many hobby and craft stores list their inventory on their websites, and some allow customers to purchase these items online. Websites such as Bizrate and Next Tag are good places to start. Simply type "plastic model trucks" in the search box on either of these websites and a list will be generated that shows you various places and prices of plastic model trucks.