I ask because it only says "Unlocked by visiting the main explore map!" and try as I might I was unable to unlock it during Pride. I figured I'd go back and try again now, given it doesn't mention anything about being exclusive to June, but I still haven't been able to unlock it via the Explore map as someone linked to in the comments of the news post it was originally announced with. I've had the Ice King show up to challenge me a few times, but no border.

Iirc I got mine at random outside of June. But with some of the current site issues it might be hindered.

Pretty sure it is random so reloading the page til you get it is the thing to do

Just in case url is https://subeta.net/explore/