Luis:
The metal strips that hold the rubber to the bumper are available new from Mobile Tradition. I think they are about $35 apiece, though my memory may be vague on this. You will need to drill holes in the strips to match the holes in your bumper.
As Chris says, treat your new strips with paint or powder to prevent future rust - the factory seem to have left them as raw steel.
I succeeded in mounting my old rubber to the new strips. The job is easy until I had to tuck the two outer ends into the bumper triangular cut-outs.