Unless you are set up for plating, it's cheaper and easier to buy them already plated (if available). Nickel plating chemicals are not cheap in small quantities, but the process itself is fairly simple. I have nickel plated some brass rifle cases, a long time ago, but they didn't turn out as bright and shiny as yours. A battery charger can be used as a power source. I have seen how the ammunition makers do it, it's called barrel plating. As I remember they were plating about 50K pistol cases at a time.