Well, since I've gotten zero response, I must conclude that this is an unusual part to break. Wilkinson has no parts, and apparently Santiago in Modena has found none either. So I machined up a couple of replacements from much stronger 6061 t-6 aluminum, with a couple of minor corrections to the (possibly defective) original design.
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.