If a contractor is not violation of the Immigration and Naturalization Act (INA), is there anything in the FAR/CFR that might bar it from using a foreign national to produce contract work products and deliverables outside of the US under an unclassified contract, if such individuals do not have access to any USG computer systems?

There are no deviations or FAR Supplements (not DoD or DHS), and the PWS does not address where the work must be done, or by whom, nor does the contract involve access to any CUI or sensitive information. The PWS is for work done in the US for an agency (not public), but does not specify who may produce work-products or deliverables, nor where they might be produced, prior to submission. The PWS does require that all contract staff sign an NDA which is very generic and doesn't specify who can and can't sign it.

A quick review of the contract clauses and provisions don't reveal anything that seems to bear on this, so I'm reaching out for any other theories or rules I may have overlooked.

Thoughts or ideas?

Foreign Nationals commonly produce work products and deliverables outside the US for contracts outside the US. So, if nothing in the contract prevents this, what is the difference? 

If you have done your research but still have residual questions, I recommend asking your contracting officer.