A quick search on abebooks turned up quite a few likely contenders, including a copy in the UK of "The Modern Kentucky Rifle, how to build your own", R H McRory, which (apparently) includes "the two original fold-out plans, one for a flintlock pistol and one of the Kentucky rifle". £25 including shipping. Vendor is Hall of Books.
A bit of imaginative searching will probably turn-up plenty of others.
(My experience of buying books etc., from USA is that it often pays to enquire directly with the vendor about shipping costs as they will often ship by a cheaper, albeit slower, method on request . But watch-out for taxes etc., upon import!)
Regards,
Phil
Edited By Weary on 19/06/2021 12:04:18