You can buy them here. On each book’s product page there is a link for a direct purchase and download from Gumroad, one of the world’s premier digital downloads payments processor.
If you need a physical copy, the easiest way is to order through a local independent bookseller or Amazon. If Amazon doesn’t serve your country–they don’t serve China, the Middle East or Southeast Asia, to name a few *small* areas–you can send us an email at email@example.com and we will have a copy sent to you directly from our warehouse.
But please support your independent booksellers!