Sorry I can't help, Neils, but it might be worth giving the guys at Vintage steel a call, they make fenders, but are pretty knee deep in old bikes, I would have thought they would have a good contact handy with bronze for that cracked casting.
https://vintagesteelfenders.com/
Let us know if they come up with anyone.
In the meantime, will keep checking my address book.
cheers,
Tim