I have had the same problem you have, because i am cheap, so never bought an air brush...
So I hand brush all the time.
To paint color like gold or silver, you really have to find a good paint that will give the effect you want.
First I would not recommend Tamiya's gold and silver (i don't know about other metalic colors), their particles are too big, not matter how you thin it out or mix it together, it just would not give you that metal feeling.
Second, do not trush gundam marker on gold and silver too, they are even worse than the Tamiya paint....
To be honest, gundam marker on the gold and silver are trash. Only the chrome silver was pretty good ( have to use it well too).
I am sure you can find something else in Hk, there are so much different brand of paint to choice from, if you are like me, got stuck in US, then try the Tester gold, shake it well, and make sure it's not too thick or thin, it gives a pretty good effect, and yes, i am talking about hand brushing.
In the end, before you paint the color on the part, just double check the paint. Usually how you can tell the particles being big or small, just shake it well, then look. You can tell the difference
Hope its helpful