Part Locations: Diner
There are three areas to the Diner which include, the Diner itself, the Gas Station garage, and the small shed to the far left. Each of the items needed to create the zombie shield are often found in the Gas Station and the Diner.
The dolly can be found inside the diner, although its location seems to change fairly often to left or right side of the back wall.
The car door can usually be found in the garage located to the left of the actual diner.