I don't know about your area, but my local Walmart sells Castrol Hypoy C 80W90 at a great price, and they're almost always open.
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.