Try these web sites of apu manufactures,they may have some info of use.
GARRETT
http://www.geae.com/aboutgeae/busine..._aviation.html
HONEYWELL
http://www.honeywell.com/
ALLIEDSIGNAL
http://www.alliedsignal.com/
Here is some of the engine manufactures(may have some info an APU`s)
RollsRoyce
http://www.rolls-royce.com/index_flash.jsp
General Electric
http://www.geae.com/
Pratt & Whitney
http://www.pratt-whitney.com/
Regards,DDG