How do I attach brackets to dry wall but there are bricks behind it. I can't find studs but hit brick.?

I am trying to install a cornice over a doorwall. It is somewhat heavy. I planned to use 4 L-shaped brackets, screw them into drywall, set the cornice on top and fasten underneath. I have installed others this way in other homes. I used drywall anchors but they hit brick.