If you want paper:
http://www.cdjapan.co.jp/searches?term.media_format=&f=major&q=sensei+no+shiroi+uso&f=major&q=&f=major&q=&order=scoreboost_cdj&range.rel=&range.sale_price=&term.caption=&term.audio_language=
The books are cheap but the shipping is very expensive...
Otherwise you can buy ebooks, there are tutroials online that show how to create an account and buy stuff on these sites:
https://www.ebookjapan.jp/ebj/209643/
https://renta.papy.co.jp/renta/sc/frm/item/71540/
(ebookjapan has higher quality images)
Since this is an award winning work, Kodansha US might decide to license it someday... I don't know if they're the type to not license stuff that has been scanlated.
Thank you!!
This book truly is a masterpiece. It's one of the few books that actually made me cry and strongly connect with the characters. I will also take the messages the mangaka wrote in the story to heart and remember them forever.
If anyone has any links to buy the actual manga so I can support the mangaka please share.