In the video
At the beginning the plate is made of tinfoil. If you don't have easy acess to sheet metal or can't get to a store that sells it you can take a thin board and fold the tinfoil over it and tape the back, then use the same instructions as before. Still an even easier plate is to just set a square of tinfoil on a table and use that. Pretty much anything that is flat, metal, larger than a piece of paper and you can hook wires to will work as a discharge plate.