There are 56 volumes of the manga. 55 comes out in December 2010. 56 comes out Jan, 2011. There are 7 seasons of the anime out in America, but the last season: Inuyasha season 8 The Final Act only came out in Japan.
you can probably buy it on the internet but if you can't find a way to buy it online you need to search for a shop with manga's and comics normally they'll be able to obtain the manga for you or they...