Most speedometer repair shops are in your local Yellow pages. Palo Alto Speedometer in N. California does this but its about as far away from Boston as possible without getting wet. They do do mail order.
PANTERA INTERNATIONAL
A DE TOMASO CAR CLUB
Presents the De Tomaso Forums
The On-Line Meeting Place for De Tomaso Owners and Enthusiasts From Around the World
Clicking on the banner will take you to the sponsor's website.