There doesnt seem to be a lot of information out there in regard to aftermarket gearbox oil coolers. Does anyone have any photos or guides on oil cooler placement to ensure decent airlflow through it without risking damage from debris etc?

I run mine just in front of the gearbox with a few brackets. You can fit a NACA duct to force the air into it. A shroud with some mesh will provide protection.

Lots of pictures of Japanese cars running them. All use "the loop" and are mounted in front of the gearbox with a mesh covered sheet metal funnel picking up air from underneath the car. 
 
Brendan uses a pump on his from memory?
 
This picture shows engine oil cooler in blue and trans cooler in black (yet to have plumbing and air guides fitted)
http://www.geocities.jp/power3580/171-7143_IMG.JPG
 
 
 

I have one like this but didn't bother putting it back on after I rebuilt the motor. Not sure if it made any difference.