You can get these for mid forties at the American Bonsai Society home page.
http://www.absbonsai.org/books/booklist.html
Your money will support that organization's efforts--which includes publication of new bonsai books.
Bonsai Techniques II is better than I, if you're advancing. It contains information on less straightforward topics like pot selection, more detailed design techniques, etc.
By the way, both books weren't meant to be books, really. The first is a collection of Naka's articles that were distributed at club meetings way back when. They are not the best articles to follow when it comes to plant care and some cultivation techniques...The books' strengths are in their ability to teach about design and trees.