The problem is, all the non-model paints, cold galvanising spray, galvafroid etc, are zinc rich paints designed to stop corrosion - they don't look anything like hot dipped galvanising where what comes out shows the bright and shiny zinc crystals which have a non-uniform visible surface and weather down into many shades of grey on one surface.
Galvafroid, visually, is just a dark grey paint.
It's damn near impossible to replicate the hot dipped effect in 1/1 scale, let alone 1/12 (or whatever).
Cheers
Lance