Small Scale Military Headquarters

I'm presently painting Toy Soldiers of San Diego's US Vietnam Marines. I have been unable to find the right green for the uniforms. I have tried Vallejo Model Cover USA olive drab and USA cam olive drab. They are not the right green. I am using Figarti, Britains and First Legion as a color guide. Does anyone have any suggestions or recommendations? The colors I have used are too dark. I'd really appreciate any input. Thanks.