Polished aluminum trim coating
I've been using MC-160 from NIC Industries on my polished pieces for a few years now and it has replaced clear powder on them completely. Customers and I are both delighted with it.
All you need is an HVLP spray gun with a .08 tip ($17.99 on ebay). It's marketed as the "World's Strongest Clear Coat" and will not yellow, fade or chip.
Once on the site, click the Cerakote Clear section. There are five different formulations -- polished metals, pvd, etc., and even a matte clear if you don't want extra shine.
NICIndustries.com