I use nail guards as practice plates. These are small pieces of steel that are used in construction. They are attached to the edge of a stud and they are meant to protect any pipes or wires running through the stud from sheetrock screws. The reason I am explaining all this is so you can describe them and find them at your local builder supply place. They are 1 1/2 inches wide, about 4 or 5 inches long and about 1/16 inch thick.
They are a little harder than the practice plates Brownells sells and way cheaper. They come in packages of 50 around here (eastern NC) and I get them at Lowes.
Regarding brass, remember that brass kick plates are not all made of solid brass. So ask, or read the package carefully.
Have fun!
Ken Moors