where are  unit records for the vietnam war kept, and are some online?

Dear Mr. Irvine,

Thanks for posting your request on History Hub!

We searched the National Archives Catalog and located 112 series for the 25th Infantry Division; 15 series for the 25th Infantry Division, 3rd Brigade; 8 file units for the 2nd Battalion, 22nd Infantry in the series After Action Reports, 1965-1972 plus Boxes 450-464 in series Infantry Unit Records, 1965 - ca. 1973, all in the Records of the U.S. Forces in Southeast Asia, 1950-1976 (Record Group 472). For access to and/or copies of these records, please contact the National Archives at College Park -Textual Reference (RDT2) via email at archives2reference@nara.gov.

We hope this is helpful. Best of luck with your research!