There are a number of companies that rebuild old instruments such as speedometers, tachometers, etc. I haven't used any of these, but I thought I would provide references, nonetheless.
Alpha Instruments - Toronto, Canada - (416) 736-4267 ask for Ted Note: I've heard of at least one customer who was less than completely satisfied with Alpha Instruments.
Palo Alto Speedometer Note: I've heard of several reports that service has gotten very slow and that returns due to any number of problems is a regular occurence.