The Greek word—yuxikoj—for natural man is used six times in the New Testament.
In I Corinthians 15:44, 46 reference is made to a psuchikos body, an organism adapted to the soul, in contrast to a pneumatikos body, an organism adapted to the spirit.
In 1Corinthians 2:14, James 3:15, and Jude 1:19 the whole self is in view or the 'natural man’ limitations are indicated by means of this terminology.
One of the designations used by Paul for the unregenerate indeed is to be found in this term (1 Cor. 2:14). They are described accordingly as unchanged from their original fallen and depraved state.
Distinctions must be drawn between the natural man and the spiritual as well as between the natural and the carnal. (See Flesh.)---Vol 7 Systematic Theology
IMHO, some additional distinction arises historically in discerning between the laws created by man for the governance of all men, regenerate and unregenerate, and the laws of the Church, applying to the regenerate. The natural law was more focused in the 15th through 19th centuries on discerning between these different groups of governed bodies.
Lord Acton also provided some letters to the Queen of England which alludes to this discernment in describing the meaning of the 'Separation of Church and State' many decades before such political enunciations in the colonies.
I'm not sure what this dissertation on "Natural Man" has to do with Natural Law. Could you elaborate, since it is less than obvious to me?