I would suggest Vietnam Order of Battle by Shelby L. Stanton if you can find it. My personal copy got lost in a move some years ago but it is an amazing encyclopedia of all things military in the (American) conflict. I seem to recall it had numerous TOEs.

I'm not sure if you're willing to physically go to a college library (I'm pretty sure there's no electronic version) but if so it's probably available either on site or via transfer from a different library.