Since 1992 I have not had time to update the book further, much though I would like to -- and ought to, to reflect the new ideas that Sôke often brings up and my changed understanding of some other concepts. I could at least tidy up the formatting, take out the phonetic signs (many people said they were too difficult, although it did help them pronounce the words more correctly than normal romanization), update the bibliography and reprint it ... and maybe I will do so when I get a chance. There may also be versions in other languages sometime (I've seen some attempted translations but none I'm really happy with). But for the time being you're stuck with the 1992 edition, costing 10 pounds including p&p (roughly US$15 - for an *approximate* equivalent please consult the Exchange Rate Calculator). This can be paid by cheque etc., or online via NoChex (UK only) or PayPal (including by credit card). If you want more details please get in touch.
Incidentally, you may find some people offering translations of various of the above books on eBay etc. There is little doubt that you can learn from these translations, but having looked at a few I'd also say that many have flaws, and many are also unauthorized (i.e. in breach of copyright), despite what they claim. I would advise you to ask Sôke first ... and/or stick to looking at the pictures and reading Sanmyaku and Sôke's official English books instead.
To give you some idea of how many books are available on the subject of Ninjutsu in general, and the Bujinkan training more specifically, here is a copy of the Japanese and non-Japanese bibliographies I originally drew up as part of Bufû Ikkan.