A few options for buying are listed below. Some readers may be drawn to the economies of the secondhand market; they can, if they like, do what readers did in the days when The Last Samurai was out of print, and send the author a goodwill gesture via Ko-fi.
During the pandemic many bookstores went through the ungodly hassle of setting up online shops; they can now take orders online and ship anywhere. I've given preference to a few terrific bookstores I happen to know of (would be happy to add to the list since I know many have been left out)
US
Everyone's Books (Brattleboro, VT)
Community Bookstore (Brooklyn)
Carmichaels Bookstore (Louisville)
Bookshop.org US (supports indie bookstores)
Indiebound (will guide to your nearest indie bookstore)
Canada
McNally Robinson (Winnipeg, Saskatoon)
UK
For e-books, your best bet is with the usual suspects: