If you can't find a new bracket that will fit, take the old parts to a good aluminum TIG welding ship and they can fix the old one up. I would grind it clean, put a TIG weld on the crack, and then put an aluminum plate over / under the old one (over the top would be stronger), redrill holes and put it all back together again. I would expect $75 charge from the welder.
2002 Newmar Mountain Aire Limited 4370 w/ Spartan K2 and Cummins 500hp
ASE Master Certified (a long.....time ago...)