http://www.freerepublic.com/focus/news/3070203/posts
It's Canon 915, and it applies to Biden and any other pro-abortion Catholic politician as well. But in any case, it's not the Bishop of Rome who has the job of issuing public excommunications to errant Catholics in their various dioceses. It's their bishops' job.
I don't know who that would be in their home states, but in Washington, DC it's:
Archbishop Donald Wuerl
Street Address:
5001 Eastern Avenue
Hyattsville, MD 20782-3447
301-853-4500
Mailing Address:
P.O. Box 29260
Washington, DC 20017-0260
The article in the thread you linked to indicates that she SHOULD be denied communion. Not that she IS being denied communion.