National Archives link
The U.S. Government is sometimes called the world's largest publisher so it's hard to decide whether it's predictable or surprising that it's been slow to embrace ebooks. Poking around the GPO website turns up many but they're mostly recent and seem to still be only a selection. There's a charge for most of them - at least one was double the price of the print book. When I was a kid the local college library was a government documents depository and I used to read collections of Indian legends there. When we were older the thrift stores around a nearby Army base had lots of military government publications including histories (though we were more interested in the tactical guides).
What's Cooking, Uncle Sam? is actually an exhibit catalog but it's full of old promotional images, photos, documents, etc so that I think it stands on its own. Plus this one actually is free.
