What is the safest way to acquire non-alkalized cocoa powder?
Without actually being able to access the ConsumerLab report you mentioned, it's difficult to know what meets your definition of safe. 



Scharffen Berger natural cocoa is one option. It has 1g fat per 5g serving, which I believe should meet your definition of "full fat". It is natural (non-alkalized) cocoa powder. It's quite expensive, and I believe normally considered "high quality". Scharffen Berger is now owned by Hershey's, which is definitely a major producer in the chocolate industry. 

I highly doubt that Scharffen Berger and Hershey's cocoa are now identical. This is partly based on personal experience (10 years ago, which is not current), but also on the nutritional information for Hershey's (0.5 g fat per ~5 g serving), which I believe does not meet your "full fat" criterion. 



Another option is Ghirardelli unsweetened ground cocoa, which is also a large producer. 


  Not processed with Alkaline/not Dutch processed.




I have no affiliation with Scharffen Berger, Hershey's, Ghirardelli, or any other chocolate producer.