If you want to get the old sea map in Pokemon emerald without cheating do have go a Nintendo event?

You are correct! The Old Sea Map in Pokemon Emerald is only obtainable through a specific event.

You cannot get it through normal gameplay. The only way to obtain the Old Sea Map is to attend a Nintendo event where they distribute it. These events are usually held in conjunction with Pokemon tournaments, conventions, or other promotional activities.

So, if you want the Old Sea Map legitimately, you'll need to keep an eye out for these events!