I have used Triple S for my RM forks and stem and they were excellent. They do have metallic finishes but it can get expensive.
LSN have a very good reputation too and I think they are cheaper - I have seen their work and it looks very good - but I'm not sure if they do a postal service. I could help with that if needed, I don't mind taking delivery of a frame and taking it there for you for fuel money.
The base coat of the metallic finish is a standard powdercoat, but they put a metallic lacquer on top to give it the finish. Triple S told me that's why it's a lot more money as it has to be powdered then prepped for spray top coats straight away.