Coating copper with aluminium powder
You are way overthinking this.  First, ever hear of companies doing chrome plating? Yes. Zinc plating (galvanizing)? Yes. Aluminum plating?  No. And there's a reason for that!  Aluminum corrodes horribly in the weather, it would be somewhat less desirable than manure plating.  

Just buy cold galvanizing compound. It is paint that's over 90% zinc,  designed to repair/restore things which were galvanized.  The remaining 10% is the resin that holds the paint together, and the solvents which evaporate. 

It weathers to the appearance of a galvanized tin roof. 

The solids are heavy and really want to separate.  It takes a long time to stir it up. It wants to separate in the paint cup while you are painting, so you must constantly stir it up from the bottom.  Also, it's liable to break a paint shaker unless the shaker is designed for much larger cans.

Seriously, the can is so heavy you want to heat it up to see if it says "One ring to rule them all". 

If you must make your own paint, don't use epoxy as a base. Sunlight destroys epoxy.  But there are several other things like epoxy which don't have that problem, and they are widely used by shops that make skateboards and surfboards.  An example is polyurethane, which comes in 2 parts, you mix it like epoxy, mix in your powdered metal base, and off you go.  

Also before you say "not available in NZ", do make sure you've done some genuine detective work. Industrial procurement is never easy.  I need a custom crankshaft for an obsolete industrial diesel, they don't sell those at Walmart and it isn't on the Internet.  You have to dig, dig, dig through the industrial supply network.