I ran into this myself back when I attempted to create new animations.
Some of the basic soldier models being used in-game do not have any source files in the "data source" folder, I'm guessing they are very old and the source was lost or not provided by the people who started the project.
Sitters and I think a few others more recently in the last year or so created some alternate soldier models, I think mostly for non-player units, which are in the data source but have not been put into the game.
I hope this sheds some light on the issue, if I'm correct.
Considering how old and out-dated the player models are, and the fact there is no source, it *might* be worth it to just create new player soldier bodies, considering the fact that people have talked about new armor and new animations, etc. Of course, this would take some modeling work.
If this idea is pursued by modelers who have the time, one tool that might help is the open-source "MakeHuman" which is on sourceforge and already has a tech preview that mostly works available for download, a totally new version that I believe has a compatible license. I played around with that program before - It can easily be used to make models of people quickly, which can be simplified easily to reduce polycount, then it isn't hard to add clothing. (And the models can go right into Blender.)
An alternative would be to hunt down the old developers and ask for the source for the player soldier models...