What about "Hammerite" (?) that's usually a good metal paint. (Google it to find out more)
It was originally manufactured for the car industry but can now be used for other items. Also they have now brought out a 'smooth' version besides the 'bobbly' one. Can be bought from quite a few outlets especially car shops , such as Halfords. Ebay and Amazon also sell it...it's not cheap but colour will last a long time. (although gold does lose it's colour fairly quick ly, compaired to other colours due to the light sensitivity)
If the gates have any 'rusted' places use "Cure rust" first, also by same company.

We always used it on our metal gates, when we had them, and NEVER had any trouble.

Christine xxx