Joe at Scale Sprints makes awesome decals, but he is kind of scaling back a little bit. www.scalesprints.com, or look up scale sprints on facebook.
Justin at Southwest Scale Chassis has a bunch of chassis parts, hoods, body panels, etc.. He's great to work with also. www.swschassis.com
The Parts Box from Australia has some stuff available too, engine parts, wheels, tires, hoods, etc... www.thepartsbox.com
This should get you started, good luck with your projects!