Where do I find shaymin?

Pretty sure you would need an Action Replay to obtain it. North eastern side of the map near the Pokemon Leauge. You'd need a "Walk through anything" code to cross a bit of ocean to get to it.

I'm pretty sure it was an event so you can catch Shaymin using an Action Replay. If you catch it with the Cherish Ball nothing special happens. So here's how to find him. Fly to the Pokemon League Use Surf to go down and into Victory Road. Follow the way until you are at the lowest point you can see and walk or run over to the man by a staircase. Go up. There should be a bridge. Cross it and go to the farthest right you can. There will be a door that you must go through. P.S. You can use the Walk Through Walls cheat code to get around this. Go to the right and there will be a pool. Use Surf. Get around the stone maze and go right then take a long way up. Keep going until you can't go up any longer. Go to the big staircase and follow the path. There will be a light. Go through the door. You are now in Route 224. Keep on going up and up and up until you see an odd-looking stone that when you examine it it is polished like a mirror. This is where you use the Walk Through Walls. Keep going up. You should be at Seebreak Path and you should have crossed the ocean. Go up. There will be a hump on the ground. Stand in front of it, facing it. Press A and Shaymin will appear.