This is a small addon I made for personal use. But after seeing this question being asked several times now, I think others might find this usefull. So I'll release this for everyone to use.
This will add all the default ArmA2 units to all three sides. So now it's possible to have the factions of one side fight each other (without dirty tricks ), e.g. USMC vs CDF or Russia vs ChDKZ. You can also use this to overcome the 144 groups limit.
At the moment, only the "normal" soldiers are included. Force Recon, MVD and Spetsnaz are still missing. I might add them in the future.
Also there are no civilians, as there already is the armed civilians addon by Wolle.