Working with brass is tough... there are several ways that brass is put on a part. You can have heavy brass plating applied or "flash" plating (I use flash plating looks more like gold when done) The problem with brass is coating it with a clear. Getting a product that will stick over time, and not react with the brass or the base metals that are under the brass. (in the flash coating we do, the part is triple chrome plated (copper, nickle, chrome) then the brass is flashed on)
Traditionally clear lacquer is used on brass, it works well but on a pinball machine dose not hold up to the ball rolling on it or the oil's etc that is on your hands. You can have them powder coated with clear, but will have to make sure the place that is coating them understands how to powder coat brass. Brass can "out gas" when in the coating oven and you can get little bubbles caught in the cleat coating, them have to put the parts in at a lower temp for a longer time to get it right, even then there is no guarantee that the part will not out gas.
I worked with a plating shop for over a year, to come up with a way to get the "bright gold" look, that has a hard yet flexible clear coating that expands and contracts as the metal moves and holds up to the ball rolling over it. It also holds up to your hands resting on it, on the lock down bar for example.
Brass looks great but is a pain to work with when coating, especially for the needs we have in pinball.