Found one.

[Clark Badgett]

Picked this up yesterday when I stopped by The Rifle Shoppe.

They had at least 4 more in stock.

[D. Taylor Sapergia]

Those fittings were common on naval horns used to service cannon.

[Clark Badgett]

Those fittings were common on naval horns used to service cannon.

Oh yes, artillery horns as well. De Witt Bailey also provides documentation of light infantry use, and pictures an “intermediate” horn he claims would be that type in his book Small Arms of the British Forces in America 1664-1815. This spout is very close to that extant example.

[okieboy]

 I am working on one of these from the Rifle Shoppe right now. The castings are nice. I wish that they or someone offered a much smaller version for a small priming horn.

[Daryl]

Taylor made his own priming horn stopper similar, but much simpler.
Maybe he could photograph it and post it?

[Clark Badgett]

I am working on one of these from the Rifle Shoppe right now. The castings are nice. I wish that they or someone offered a much smaller version for a small priming horn.

These could be shortened if you wanted to go that route.

[Tim Crosby]

  Somewhere and I can't find it I saw a horn that was supposedly made for the Lewis & Clark expedition that had a tip like it. Here is one David did a couple years ago.

  Tim C.

  https://americanlongrifles.org/forum/index.php?topic=49843.msg494249#msg494249