Contact cajon builders directly to find cajons made made in the Vietnam. Unfortunately many music stores and big online stores only carry imported brands. Buying a locally made cajon cyles your income back through your local economy. Below are links to 9 cajon makers in Vietnam:
Minimize the carbon footprint of your cajon purchase - buy a locally made cajon directly from the cajon builder. Most imported cajons are shipped around the planet in big cargo ships. A locally made cajon helps your local economy and demonstrates that you are thinking about and helping local craftsmen.
There are at least 9 cajon makers in Vietnam. Use this page to help you find the best cajon in Vietnam for you."
YouTube playlist of cajons made in Vietnam:
Note that not all manufacturers have current YouTube videos. The list on this page includes websites and Facebook pages which may contain videos not on YouTube. The list on this page is actively maintained, the YouTube playlist is less frequently updated.
Listed above are links to the cajon drum builders in Vietnam as retrieved by Internet searches in March 2018. I am sure there are many others not listed. Please send me updates and correction if you have additional information. Thanks.