I'm not clear on what "goldy" colors you mean, but here's a couple of things that have worked for me:
. Mix in some cigarette ash with your paint to give it that "flaky" look
. Add just enough water to a metal coffee can to cover the bottom, then drop in a piece of steel wool and let it sit for a few days. You'll get plenty of real rust when the water evaporates.
. If you don't like the straight rust color, try mixing Armour Red Brown, Armour Yellow and Leather till you get what you want (I use Polly-S or Humbrol).
Hope this helps
Art