I went to a Chinese grocery store that featured small supplies of Japanese, Korean, and Thai things. In their vegetable bins I thought I found Korean radish. The lady at the counter said it was, so I bought two. (Though the lady was Chinese and not up on anything that wasn't.)
They didn't look anything like the pictures in Maangchi's ingredients, most of them were skinnier and all of them were a bit rubbery on the outsides. But they were clearly not daikon and definitely radishes. Since cutting them up, the outsides were very stringy and bark-like, and didn't fully come off with just peeling. I had to cut a great deal of the outside off.
How does one know if they have a real Korean radish, and do all real ones look like Maangchi's photo? I think I got a pair of duds.