Contact cajon builders directly to find cajons made in Portugal. Unfortunately most big online retailers and many music stores only carry imported brands. Buying a locally made cajon cyles your income back through your local economy. Below are links to cajon makers in Portugal:
Minimize the carbon footprint of your cajon purchase - buy direct 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 support local artisans.
TukenTuk Cajons are located in Gaia and Make Mu cajons are located in Torres Novas.
Listed above are links to the cajon drum builders in Portugal as retrieved by Internet searches in March 2018-2019. I am sure there are many others not listed. Please send me updates and correction if you have additional information. Thanks.