I saw a used AR at my local dealer's with a lower marked "Vietnam Limited Edition". It had the outline of a map of Vietnam.
I thought it was kind of cool. But I'm pretty sure it was not all original 'cause it had a free float handguard tube. I would expect the old triangular guards on something like this.
Any info on this one would be appreciated.

I have never seen or heard of an Oly factory produced Veitnam special edition, but these types of commemerative rifles were (maybe still are)popular or common in the late '80s & early '90s and were marketed by several 3rd party companies using many of the brands available then (BM, Oly, Colt, PWA ect.).
Might try the Oly web site or the Oly Owners Assoc. (ww.oa2.org) although both sites have been rather slow the past few months.