I'm a bit surprised at the general lack of of Vietnam USMC with M-14, other than as an afterthought, or mixed with M-16 armed figures in packs. They used it from 1962 through to 1967 (or 1968 according to some) as their primary infantry weapon, so you'd think there'd be more figure ranges carrying them.
Having said that, the ARVN is very under represented in some ranges too, it's almost like they weren't there. What ranges there are are largely M16 armed too, despite the survival of the M-1 Carbine, M-1 & M-3 SMGs, M1 rifles and BARs in many units well into 1968 in most units that weren't part of the general reserve or Airborne and Marine units.
Now where can I get a 1/56th scale Walker Bulldog? Oh... that's something else...