Right, there weren't any. However, I ran across a page that mentions a number of made-for-TV movies that were indeed produced during the Vietnam War:
http://www.tvacres.com/broad_vietnam.htmI think, for the purposes of the original question, a TV-movie is just as "good" as a TV series; it's still a televised fictional work on a war that was still underway at the time.
The page is one very long, hard-to-read paragraph, so here are some highlights...
Made-for-TV movies produced while the U.S. was still in Vietnam:
The Ballad of Andy Crocker (1969) is the first made-for-television movie to deal with the traumas of the returning Vietnam veteran. ...
The Forgotten Man (1971) starring Dennis Weaver, Anne Francis, Lois Nettleton about a returning Vietnam POW veteran who finds his home changed and his wife remarried ...
Welcome Home, Johnny (1972) starring Martin Landau, Jane Alexander, Brock Peters about a Vietnam veteran who returns to his hometown that he dreamed of while a POW, but can't find it. ...
(I remember "Welcome Home, Johnny" -- and have never forgotten the town: "Charles, Vermont"!)
TV movies that just missed the pullout date of 1972, or are fairly early examples of Vietnam TV-movies (see link for synposes):
Sticks and Bones (1973) Cliff De Young, Tom Aldridge
Green Eyes (1977) Paul Winfield, Rita Tushingham
Just a Little Inconvenience (1977) Lee Majors, James Stacy, Barbara Hershey
My Husband is Missing (1978) Sally Struthers, Tony Musante
Friendly Fire (1979) Carol Burnett, Ned Beatty, Sam Waterson
When Hell Was In Session (1979) Hal Holbrook
Earliest TV series listed:
The short-lived military antiwar comedy THE SIX O'CLOCK FOLLIES/NBC/1980 is the first series set during the Vietnam War. ...
In the fall of 1987, the military drama TOUR OF DUTY aired on the CBS Network. ...
The page also mentions (and offers brief synopses of) a handful of TV specials/documentaries on the war -- which has nothing to do with the original topic, but may be of great interest if you care to hunt them down (note the air dates going back to 1964):
VIETNAM: THE DEADLY DECISION (4/1/64) CBS
LETTERS FROM VIETNAM (9/10/64) ABC
THE AGONY OF VIETNAM (8/25/65) ABC
VIETNAM: DECEMBER 1965 (12/20/65) NBC
WALTER CRONKITE IN VIETNAM (2/27/68) CBS
THE SELLING OF THE PENTAGON (2/23/71) CBS
POW's: THE BLACK HOMECOMING (7/27/73) ABC
7,382 DAYS IN VIETNAM (4/29/75) NBC
I doubt many of these docos are available for sale; however, I've had extremely good luck with the Museum of Television and Radio, where you can sit in a semi-private booth and watch tapes of programs that are absolutely impossible to find anywhere else. The MTR screening rooms are physically located in NYC and Beverly Hills, and open to the public (of course, you have to pay). And the Web site is
http://www.mtr.org/HTH!