painting my 71 dart bumpers...

Same process for anything metal. sand prime paint.
If the chrome is flaking off you might have better luck sand blasting them first.
I painted mine after seeing that the PO had blasted the chrome off and used bed liner paint on them... :( Mine are just over 18 months old and have a few chips on the front one.... I painted them off of the car and had no issues with getting them shiny (body color) I would have painted them silver or something but I thought that would look too much like a work truck. They were black (textured) and looked like undercoating or abs plastic...

That being said any more damage you do to them from sanding / blasting will have to be fixed before they get re-chromed and that may add some cost so call a chroming place and ask them before taking a sanding wheel to them..