They are using a .sux extension and the file starts with SUX3
For example border\levels\russianborder\textures\characters\3pnew\eu\eu1\eu_ass_face.sux
should look like this
This png was extracted with TexMod from the singleplayer missions.
The files I'm trying to access were for the online part of the game which no longer loads.
Edit:
I'm not sure if they are compressed. I found a default.sux and a default.tga in the same folder possibly the same file only compressed as sux?