Cascam:
I realize your post is a couple of months old, but I also noticed no replies. Here is the info I have on the rigid borescope suppliers approved for the GE 90.
An approved Rigid Borescope Kit exists for the GE90.
The GE Drawing Number for this is 9C 1174.
Seven vendors are listed as follows .
9C1174 PO1 Olympus
PO2 Everest VIT (formerly Fibertron)
PO3 Machida America
PO4 Richard Wolf
PO5 ITI
PO6 Efer
PO7 Lenox
I would guess if you contact any of them, they should be able to provide you with specific scope models, etc. Good Luck,
RVTMan