Hi,
Get a copy of Bailey's "Small Arms of the British Forces in America 1664-1815". Here is a quote from his book on page 69:
As a group, British Ordnance musketoons and blunderbusses are undoubtedly the rarest of British military longarms. No examples have been identified with dates later than the early 1720s at the time of writing."
There are references to "musketoons" set up John Hirst, Loder and Waller, and Nock during the 1770s-1800 but none of those guns are known. The early musketoons identified are all sea service. The Pedersoli Brown Bess "musketoon" is likely a fantasy.
dave