Hi blp30250,
Welcome to the Heartland Owners Forum. I think I recall seeing a project description somewhere (not sure if it was on this forum), where the owner made fenders out of sheet metal.
The problem with replacing fenders without using the same part, is finding something that fits and is stronger.
Alternatively, if the problem is cracks around the mounting screws, some of us have reinforced the back side of the fender, where the screws go through, with a thin layer of moldable epoxy covered by Gorilla tape. The epoxy and tape spreads the stress load caused by vibration. I did that in Oct 2016 and they've been holding up ever since.