Quite a few of the Pantera parts vendors stock these. Your later switch takes a different key than the early ones and is still an available factory item, I'm told.
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.