You should be able to find one in the aftermarket (car restorer market), try a
google search for malibu, bumpers, parts.
Also try
www.craigslist.org and hunt under car parts catagory.
Or try Year-One or the Paddock or one of the chevy only parts suppliers, again
try a google search for them.
A bumper shop should also be able to straighten and re-chrome your old one
but that is usually in the $150-180 price range.