It would be worth talking to your local guys, they probably have a shelf of stock colours but who knows if they'd sell you a small quantity.
So while 'researching' the how to you have to think
# Is there an alternative paint
These are all in the same family of paints, sprayable with a ceramic content.
Norrels molyresin crops up in searches but it's get very limited coulour ways, no gold and no cheaper. Mostly available in the US and used as a gun finish.
Duracoat, again crops up but again is limited in colours, the only near metallic they do is a burnt bronze that's matt and too dull a colour.
Sprayable expoxy might be an option, wheel paint springs to mind as the colour ranges will cover a gold type finish, Stardust colours do rattle cans of this for about £43 a shot of a
gold colour. They also do a liquid metal paint which is cheaper but more a 2k type paint
# Is it feasible to anodise the casing?
First pro is it is a tighter bond to the material than paint will be but the drawback is the colour range you can achieve is much more limited.
I'd go with cerakote or the wheel paint and be quite likely to farm it out to someone who has all the kit and experience to do a good job. Stripping epoxy or cerakote would be a real pain if it didn't come out as expected.