Mikael,
You have a series III car, so shouldn´t it have the same steering set up as the Maserati Quattroporte III? In that case you could find the part from the maserati vendors, for example the Maserati Source.
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.