Colt no longer offers any service for guns this old.

Here's some places that offer high quality gold plating for guns. Note that guns are "different" so pick someone who specializes in firearms.

Custom Gold & Silver Plating, Antique Finishing: Reliable Electroplating: Chartley, MA

403 Forbidden

Welcome to TechPlate, Inc. Firearms retail plating price list

Elite Custom Plating --  Re-Finishing, Custom Work, Competition Guns