http://www.spoilers.com/accesscustom/toymr290.htm
It's gonna be hard to make, I don't know what you can base it off of, I guess you have to start with a blob of putty and start molding. It's not the scoop mouth that's gonn be the hard part, the hard part is where it goes nest to the engine covor (hood or trunk, whatever it is)
Off topic: my brother had one of those on his Mr2, whenever someone asked "what is it?" He replied, "it's a rocket launcer"