The belt and its pads are simple- a military surplus belt of proper width and color should suffice. Pouches are frequently seen on either side of the buckle in front, and the pads underneath the front and back can be sewn from nylon or canvas. Add belt loops, and it's simple.
The drop-leg plates are an actual military item as well, and are available for around 20-25 USD each, or they as well could be fashioned cheaply from canvas, thick foam, and strapping.