The Rifle Shoppe makes Early British Rifleman’s Powder Horn Spout, item 853 in their catalog. I know they can be difficult to reach but I’ve had luck calling on Tuesday mornings.
From their catalog:
This is the early British Powder horn spout seen on the French and Indian War and Revolutionary War powder horns. Also seen on many Early U.S. horns. This was the standard British Riflemans type horn up until the Baker Riflemans horn with measure and the U.S. Military horns until the adoption of the metal flask type.
Here is a flat horn I made from the castings…
