I was looking for it after reading the post, but there seem to be so many different versions and edtions. Harper, Penguin. College. The New. The Concise. The International. Some say they’re organized alphabetically. How do I know which one is the kind that the article talks about, if I buy used online and cant look into it?
Are you in the USA? It's because Roget as a title isn't trademarked there so it's accepted as a name for any thesaurus.
If you want the latest edition of the "real" Roget's, it's the one published by Longman.
The one in TFA is Harper and Row, and the later 8th Edition, published by Harper Collins, is also organized the correct way. I think you'll be safe if you can get a Harper version.
That's the one I have. I've had an older version in the past but misplaced it years ago. This one does the trick, but like the article author says: it is a weighty book. (I like that.)