I bought AC Delco 18J3815 hoses from RockAuto, but they have the same brake line end threads as what you're finding. It wasn't an issue for me as I was building new brake lines, so just used the matching fitting. I can't be sure because they're gone now, but I believe the original hoses were the same. Do you have enough brake line that you could cut the flare off and get the larger thread fitting?
