Phil,
The plating shop I use has a new zinc finish called "dull zinc". I say new, it's been in use for about three years. I prefer to glass bead blast everything I send and keep it super clean - no fingerprints (oily hands leave marks). That combination replicates cad plating closely. There is a technical problem with standard zinc plating for ash trays, the zinc has a tendency to be deposited on the outside of the ash tray. The inside gets some plating but to get a decent look inside, the outside will have to get more. There are fixtures used to deposit zinc on an inside surface but they get expensive.
Jim