I own a .38-55 Lever Rifle and the ammo is not readily available now or when I purchased it. I got together with a bunch of Cowboy Action Shooters years back and we contacted Starline to see if they would produce a run. They eventually did and we all purchased enough that we will always have a good supply to reload.

What I am saying is maybe if enough .375 owners contacted Starline, Winchester, etc. they would consider doing a run of Brass - even if they won't actually do loaded ammo. It's worth a call. I have no idea how many would have to be ordered to get them to do so, but you will never know unless you ask.