given the year of the trailer, the original MFG has likely long gone the way of the dodo. You will need to fabricate or have fabricated that new piece. You are in luck though, as what has crapped out appears to just be a simple section of box tubing with the roller brackets welded onto the ends.
If it were mine, a trip to the local hardware store for some appropriate sized box tubing and about 30 minutes with a cutoff wheel, drill, and welder would have one good as new in place of the damaged one.
