I'm not sure if he still handles Panteras or not, but Cory Gehling from Collector's Choice is up near Madison, Wisconsin - about 2 hrs. out of Chicago. It might be worth an inquiry.
Here's an email address: collectorschoice1@tds.net
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.