Please navigate to the corel.com home page and use the navigation from there.
You will be directed to this page for accessing patches&updates of the Corel products:
http://www.corel.com/servlet/Satellite/us/en/Content/1152796559943
The Corel DESIGNER Technical Suite 12 patches are actually listed in the "Most popular" section as quick access.
Best regards,
Klaus.
Klaus Vossen
Product Manager, Graphics
Corel Corp.