There is documentation for the use of priming horns (actually repriming horns to be used in case of a flash in the pan) by some military units. Use of priming horns by civilians, however, seems to be a rare exception. They just don't show up in the historical record ,written or otherwise. Finding an actual example to copy is problematic. Horns that were originally thought to be priming horns turned out to be salt/spice or possibly day horns. Bottom line, there just isn't much to go on for producing a PC priming horn so find out what your customers want and go from there. Link is to the Horner's Guild website.
http://www.hornguild.org/