The lip where it attaches to the fender is on the fender. The mounting flange itself is flat and spot welded to the lip bent on the fender. I don't have my fender handy to look at, but a worst it has an upset portion that could easily be hammered into the flat patch.
I doubt there will be enough demand for someone to supply a patch for that section of the fender, but they should. That's a very common point for rust outs.
