There are a ton of pictures in the book by Shigeo Sugawa, but the $40-60 book is all written in Japanese. Really depends on the
Teppo you're producing, as not all models had tapered barrels or even those with the cannon muzzles - quite a HUGE variety actually. Like our longrifles, they progress from the plain
Shimmel up to a fancy inlaid/carved
Golden Age flint longrifle.
Stock octangular barrels, from sources like Colrain, etc., could be used. Or, at an expense, have Ed Rayl or Bobby Hoyt custom profile a cannon-muzzled barrel for you.
FYI, you can buy plans for a Tanegashima build from
Old Guard Manufacture (Poland), for maybe 30 Euro or so, but realize they (like most of Europe) does 99% of their bizness from Facebook. Presently they have a serious problem getting barrel steel in their country [due to the war in Ukraine] and if they bought a US-sourced barrel, say co$ting $200 here ... with shipping and customs, it would be 2X that, or more, before they even passed on that price to you. They are now building people custom arms to a 'stock or known' profiled barrel, where they make it
without a barrel ... then you buy one and configure it (tenons, sights, etc.) and attach it here (pins, inlet, fitting, etc.).
Link to some Old Guard Manufacture info on here =
Locks & Early Arms from Old Guard Manufacture, Poland