He's looking for a Daniel Wesson type rifle. Daniel Wesson made target telescope rifles and the one owned by the Smithsonian was carried by Edwin Stancliffe, a member of the First New York Battalion Sharp Shooters.
BTW: Attend the NMLRA Chunk gun matches. They're today's equivalent of those target telescope rifles. Apart from optics, they're close to the same.
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!