If you are on 1.0, they won't show up (they were added in 1.2 iirc?). That could be a problem. Otherwise, no, you just need to ground pound on the correct location, which is on the side of the circle in the pool closest to city hall.

You might have to either beat the game first or link nintendo network id

Fairly certain it has nothing to do with beating the game, you just have to be on 1.2+

It definitely works in the normal route of the game. Either you don't have the correct version, or you're just missing the spot