Okay, I figured out how to do this.

Click on the publication menu, and select “Followers”. Here’s an example from my menu

Or, if you prefer URLs, you can just type in https://medium.com/<your publication>/settings/followers.

That’ll get you a page with the list of followers. I think this is newly added, though, because I don’t remember seeing it before — specially not when my question was first posted.

Although I do remember seeing a list of followers somewhere. Maybe it was removed in the middle and added back again? Anyway. Problem solved. But if anyone figures out or remembers what happened, do let me know!