There are several types of service providers who will apply custom graphics to trucks, including local auto body shops, auto paint shops and national chains such as Fast Signs. Depending on the complexity of the graphic being applied, the level of expertise required by the applicator will vary.
Companies such as Fast Sign specialize in signage and banners, including custom graphics and wraps for trucks and other vehicles. Local auto body or paint shops do either sorts of work as well, but are typically capable of applying custom graphics. Graphics are available from websites such as phoenixgraphix.com and decalfx.com as both stock designs and custom graphics.