I'm not sure what you mean by "alt-right..." Usually that means something specific (For a good summary see https://www.youtube.com/watch?v=MHXL00wY3nY). Among the people who have written about how the National Socialists were socialists is Jonah Goldberg (see https://www.amazon.com/Liberal-Fascism-American-Mussolini-Po...), whom you might not like, but is not alt-right, in that he disagrees with the alt-right on almost everything.