|The short answer
is "I don't know". The long answer is that it depends on the book.
Check my Bibliography pages
and my Bookshop page.
Mas Oyama's early books are probably as easy to find as snail toes, only a bit bigger. If you're lucky, your Shihan or Sensei may have a copy (possibly even signed by The Man himself), and if you're reeeeal good, he might let you have a look at the cover, after you've fasted for three days, scrubbed yourself clean, had a shave and a haircut, and said the dojokun in Latvian one thousand times, (unless of course you are Latvian, in which case use the Basque version). You will note that neither is available on this site. Finding them is also part of the task!
Essential Karate and Vital Karate, his later books, are available in most good martial arts stores, and are apparently very good too. I've got copies of each, but have no basis for comparison, since I haven't seen the earlier ones. There is a review on Amazon.com Books. Search on Author (Oyama) and Subject (Karate).
Steve Arneil's books are available from the IFK honbu in the UK. See the Bibliography pages for details.
If you're looking for anything else, try asking on the Ichiba.