Alright I whipped up something hacky looking to start with for the map request. There's now another cave entrance in Mayday Village that takes you to the Find-a-mon islands.
Walking in there will take you to the first area. It looks something like this:
The middle door takes you back, the right door takes you to the next area. The sign tells you what mons you can find. In the grass you'll find Boatborn, Boatforged, Boatmurdad, and Uncarp and in the bushes you'll find Skelfish and Urwhal. I could only put two mons in the bushes because the chances of encountering mons are hardcoded so you have a 60% chance to encounter one mon in water (which is what the bushes are pretending to be) and the next biggest chance is 30% and each bracket gets smaller after that. You end up with a 25% chance of each mon in the grass, though, because there are more and smaller brackets.
The second area looks identical to the first because of a stupid two-maps-using-the-same-image thing that I took advantage of to cheat and be faster. There's a dude blocking the right door in that one so you can only use the middle door to go back to the first island. This island has all of the unicorn mons in the grass and Espier/Helgust in the bushes.
Hopefully this works for people for now, I'm planning on making a better version with dialogs where you get to choose which mon to fight rather than making it random, but this was quick and easy for me and should be easily expandable until the better version is in place.