The post links to Harper's hosted scan of the original printing but it's a little difficult to read. There is a copy meant for screens [2] (under the title Authority and American Usage, subtitled or "Politics and the English Language" Is Redundant, as it was published in his collection of essays Consider the Lobster[3]).
[0] https://news.ycombinator.com/item?id=23581841
[1] https://en.wikipedia.org/wiki/Garner%27s_Modern_English_Usag...
[2] https://github.com/borges-paradise/DFW/blob/master/dfw-autho...