Well perhaps not unobtainium, but large pots of metallic paint.
Unfortunately just two colours, turquoise and rusty pink.
But the turquoise is very shiny.
Large pots with 28mm em4 figure for scale :

The label fell off the turqoise pot, but it shows how much the paint has separated.
Needs a lot of stirring.
It's actually a Dulux household paint, hence the large pots.
(But who would paint their house metallic turquoise ?)
Test painting on a Scheltrum VSF vehicle:
the paint doesn't show up as shiny in the picture as it is in real life.
Both colours applied over a matt grey primer.

And then some test painting of just the turquoise, em4 robots undercoated in matt white, Old Crow scenery in matt grey:
