I had gotten mine from Wilkinson about a year ago but upon checking his site it looks like he may be out of them?
With him though you need to talk to him to verify anything anyway, so call him.
There are at least two kinds that I know of.
The most recent are round like what I have. Pictures of '74 US cars seem to be square with rounded corners?
These are the ones I got from Wilkinson. I'm told that they originate from BMW.
(Incidentally, the a/c vents vary also)
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.