I thought I read somewhere that a Camaro one will work with a little trimming.
Did you try
http://firebirdman.com ? He usually has a few parts cars going. You could also post over on
http://firstgenfirebird.org/ubb/ubbthreads.php and
http://forums.performanceyears.com/forums/
Other places:
Chicago Muscle Car Parts
Frank's Pontiac Parts
Don