I think you can find it at the Department of Homeland Security.
At least that is so, according to CBS News: https://www.cbsnews.com/news/coronavirus-gun-shops-essential-service-trump-administration-says-same-as-businesses-grocery-stores-pharmacies/.
But I couldn’t find corroboration at the DHS site....
But if CBS is correct that DHS has ruled firearms and ammo “essentials,” like food and medicines, etc., wouldn’t that be ironic???
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There was an article posted on the Forum that stated the Feds had stated that firearms and ammo business is essential. It was posted shortly after some of the states had decreed that those businesses had to be closed.
I don’t recall which Federal Agency published the ruling.