Dear Mr. Fowlkes,
Thank you for posting your request on History Hub!
In order to search for potential information in NARA’s records, knowing the unit and dates when it occurred is the key, as you note yourself in your request. Once you determine these pieces of information, please check the USMC Command Chronologies for Marine units in Vietnam. There were several reconnaissance units including 1st and 3rd Reconnaissance Battalions and 1st and 3rd Force Reconnaissance Battalions.
We hope this is helpful. Best of luck with your research!