Michael Schoeman's Springbok Fighter Victory, Volume 6 is listed as available on the Air Britain website. It is also available from The Aviation Bookshop.
http://www.aviation-bookshop.com/hub.htm
Stan Bishop & Bruce Hoy's Losses of the 8th and 9th Air Forces, Volume 4 (covering July/Aug/Sept 1944) is listed on The Aviation Bookshop website. They tell me the book should arrive about the first week of July. They also list a limited reprint of Volume 2 (Jan/Feb/Mar 1944). I do not know if they have Vols. 1 and 3 available, although they are still listed on Bishop & Hoy's website
http://losses8.webplus.net/
I have both books on order. Both series' are excellent.
Enjoy!
Frank.