Cheers Keith,
http://www.h4.dion.ne.jp/~t-ohmura/gunto_002.htm
Here is a nice lot of information to read through on military swords of Japan
Or as suggested by Franco ,Fuller and Gregory,Military Swords of Japan will help also.
Take your time to read and study ,there is no shortage of Showato Gunto out there for $1000 or a little less in pretty good condition.
Some are obviously more desired than others,don't let the fact that a couple of seppa are missing or a catch is buggered etc put you off a particular sword,those are all little things that can be picked up around the traps.
Look long and hard at the blade as well as overall package.
Best of luck
Moss