Contact Anderson Silverplating (
Anderson Silver Plating). They're the best in the business and the exclusive choice of almost every domestic horn maker. They also make the Schilke "Beryllium" bells. I had a classic Couesnon flugelhorn plated by them about 20 years ago and they did an absolutely perfect job. If you intend to send them an instrument to plate, it's definitely worth a call in advance to determine price, shipping requirements, and wait times. Good luck.