Have you tried Steve Wilkinson in Paramount, CA? I know he just found a bunch of New Old Stock sheet metal at the factory in Italy. I don't know what he really has or the pricing -- but it may be a resource to at least check. The best way to get in touch with him is by giving him a phone call. He is not good at getting back via email. You can look up his phone number at his website Pantera's by Wilkinson.
Best of luck.
Mark
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.