There was a Muzzleloader article on them for sure.
It was in the May/June 2016 issue about making
A Pulverhorn.
I started with brass castings from the Rifle Shoppe.
These flasks were commonly used by French and Spanish
Soldiers here in North America
Back issues of the magazine With My how to article and
info on how to order It should be available from Jason
over At the magazines web site.
And yes, home made versions can be crafted with out
Brass fittings too. Here is a version I cooked up awhile
Ago for myself . It has a turned horn spout and a copper
Thimble measure.
TC