I haven't been into this part of the car in a while and I may be mistaken but I think the caps from a 66 or 67 Mustang fit those hubs?
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.