There is one of these...
...a Albertish horn, in the museum at the Norwich University in Northfield VT. It is in poor condition, and without a mouthpiece, but there is a photograph of the school's mounted military band that has a player seated atop a horse with the thing at the "high port" position.
The horn is a "no name" instrument, roughly of "classic" bass clarinet dimensions (i.e., to low E rather than to low Eb for doubling A bass parts), is brown in color, and had a plated brass crook and bell. No tuning slide that I recall. It also stank to high heaven, as many older instruments do. It had not been "conserved", but rather just accessed and then put on display.
Norwich University, which used to be located in Norwich VT, but for some reason had to move, was one of the original "military schools" authorized by the Federal government to supplement the production of officers at West Point - sort of an early form of ROTC. As near as I can tell, the Citadel was the one authorized for the production of infantry officers, the Virginia Military Academy was to turn out artillery officers, and Norwich University was to produce cavalry officers. This was a very smart idea when classes at the 'Point were barely large enough to replace resignations from the officer corps, never mind the demands of the Seminole and Mexican Wars.
But, as anyone who has ever visited the state knows all too well, Vermont is not horseback country, much less cavalry country. Unless you are in a river-generated ravine or valley (in which case you would be swimming), you are always walking either up or down, or are moving about with one leg perpetually bent.
Just which leading military mind assigned cavalry to a school in Vermont has never been made clear to me, but I'm glad he's now long-time dead - our military has enough problems without the likes of him. Some logic behind the selection may have been due to the fact that Vermont was a rare Democratic stronghold in New England during an era when the place was pretty solid Whig Party.
(The student parking lot has a total of one hundred and thirty-five vertical steps that have to be negotiated before you are at the same level as the classroom buildings and dormitories. I know this because I counted them both going up and down...)
Incidentally, although the school is no longer strictly a military school, they still have a sizable cadet corps, and they still train as cavalry, although the tank and the armored personnel carrier have replaced Dobbin. They also have their own dedicated ski lift, and train as mountain infantry during the winter months.
(The other odd place where the Army has deigned to place armored units is in West Virginia. The place is about as vertical as Vermont, but nonetheless you drive along their kinky highways and - voilá! - there is a national guard armory with a couple of modern tanks parked out in the paddock. Go figure...)
Famous graduates of the place include Grenville Dodge, the railway magnate, and Admiral George Dewey (once again, go figure). Neither played in the band.
They had no mouthpiece for the horn, or I would have tried it out. I didn't have my horn, but I had my mouthpiece (which would not have fit) plus my reeds and ligature (which would have).