Have you ruled out brass completely? If you find brass buttons in the right shade they can be a more subtle choice than both gold and silver. My first hand choice, if I were to chose buttons for a new blazer would be horn though.
I'm fond of the silver oxide as well, but a gold-toned brass would be the proper, classic match-up for a classically cut deep navy blazer. Could you provide more information on the blazer itself? A photo would be great.