Here are two books on SW i bought in Japan
Macaroni Western no subete (All the SW) 324 italian films writer Kazuo Kajiwara
Book in Japanese (2002) 2000 Yens (20$/15Euros) ISBN4-89172-665-2
There is a short description of the SW made from 63 to 76
With an short annex for actors/directors/music
Many B&W pictures some i only saw on this book.
7 color pages with various SW covers.254 pages.
Macaroni Poster Taizen
Very good art book i found in a 2dHand book shop
English/Japanese with postface by Franco Nero Writer Katsumi Ishikuma
(2001) 3800 Yens (38$/27Euros) ISBN4-89691-568-2
Old edition maybe not easy to find, i was lucky i was not looking for SW stuff when I get it.
An art Book with more than a hundred full pages SW posters all color
from Italia/US/Japan/and so...