You can get a decent machined finish by laying down a good gloss black (my go-to is Rustoleum's Professional Grade -- it's made with ground up ABS dissolved in suspension, so once it's cured you've basically coated the thing in smooth ABS plastic); then paint with the best fine-grind metallic paints you can find. They're getting harder to find, now, but my personal fave is still Testors airbrush Metallizers. I'd have to experiment with others that are available. I change up the order of operations by putting the sealer down first and, while it's still tacky, spraying on the metallic coat.
Once it's all cured (sniff it and it doesn't really reek of paint fumes any more), stick a dowel in the emitter end, chuck it into a drill, and, while spinning it, burnish it with Scott's shop towels or 0000 steel wool or 1000-grit polishing film or a buffing wheel. Spinning it grains the finish while polishing it, so it ends up looking like it's been shaped on a lathe. It can take some trial and error as a new technique, so I'd definitely recommend practicing first.