Where do I find something that looks like that — shortened silver barrel with air tube.
Ignore the Import Ban thumbhole stock.
The kid's barrel was cut right ahead of the gas block, right near the front sling swivel.
Put your finger over this picture to cover the muzzle end of the barrel, and you have something that looks exactly like the gun on the ground.
But this one will kill you.
All that's needed to accomplish that is a hack saw and file.