It is called the lock pillar trim.... I think I found a source for them the other day...
http://www.gmpartsoutlet.net/?i=2&make=116&model=667&year=1996&catid=30188&subcatid=32116§ion=128&type=parts
or,
http://www.gm-auto-parts.com/ifrm_browse.php
If I read correctly, they have them...