I am not aware of any of Sebata Yūzō's books (瀬畑 雄三 |本) that have been translated into English.
I am a little unsure of just which of his books you are looking for.
You can do an internet search with this Japanese phrase, 瀬畑 雄三 本 , or 瀬畑 雄三 の本, = Sebata Yūzō books, and probably find every book , video tape, DVD, etc that he has authored, been in or otherwise credited as author.
However. I am guessing you may be looking for this book:
渓のおきな一代記 単行本 – 2010/10/22
Kei no okina - ichidaiki tankōbon[ which I think translates as - Old man of the Valley (or River) - biography paperback book].
ISBN-10: 4622075660
ISBN-13: 978-4622075660
https://www.msz.co.jp/book/detail/07566.htmlOne of his books is on Amazon (US) but maybe over priced. But out of print books are sometimes high priced.
It is this title - 源流テンカラ釣りの知恵 (渓の翁、瀬畑雄三の遺言。
Something like - Headwaters tenkara fishing wisdom. (River/Valley Oldman, Sebata Yūzō's testament)
The book - Kei no Okina , appears to be out of print. But used copies available from several places.
The listing on Amazon (Japan) also appears to be used books, with a from (より,yori) price in JY.
You might be able to find a website where it is easy (less difficult) to order it from by doing an internet search of the title, 渓のおきな一代記 単行本. Or search for a different title if that is not the book you are looking for.
Or order it from Amazon (Japan) . I do not know how to. but I've read it is easier to do today than in the past.
Probably the easiest way to order it is have Keiichi Okushi at tenkaraya website order it for you.
Books are heavy. Shipping charges for books shipped from Japan are sometimes as high as the price of the book. Unless you can make the shipper understand that you want the lowest price shipping and do not mind it if it takes a month or so to get the book. Getting a book in 5 days to so cost a lot more.
fwiw, if I recall correctly, and I may be mistaken, this book has a lot of text, only a few diagrams. One of his other books, has more diagrams, with simple Japanese captions. Easier to get more out of the book if you can not easily read whole pages of Japanese text. But I don't at the moment know where his books that I have, are located. Other wise I would take a quick look and verify which book I am thinking about.
Hope this helped.
Good luck.