When I go to wally world or any other store that sells toys for that matter, I always look to see if they have issued any Nitro models in the Hot Wheels or Matchbox line. (I am always looking for Challenger items too.) So far, no luck on the Nitro.
My wife commented the other day that one of our son's plastic Mega Bloks toys looks kinda like the Nitro. A bit of a stretch, but maybe if I paint on a crosshair grill... This is probably as close as you're going to come until someone licenses the design from Chrysler: