I would check local fabric and upolstery shops. You can do it yourself as it is (at least on my 71) just a heavy felt. Easy to form and to glue with spray contact fabric glue.
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.