It looks like any 12mm x 1.5 acorn lock lug will do the trick. I ordered a set by Dorman and will follow-up with how they fit (for those interested).
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.