The most authentic finish would be brass electroplating. However, this is a complex process requiring pre-treatments like degreasing, zincating, nickel plating, and then brass plating. This is not something that can be done at home by an amateur, but any company doing electroplating will be able to assist.

The cheapest option would be to anodize and then dye with a brass-colored die. The obvious disadvantage is that the characteristic aged look for brass cannot be achieved as the brass anodizing won’t react with the to produce the depth and texture that you are looking for. You can also use specialized paints.