Stuck in Pokemon Pearl?

I haven't played this game in a while, and I forgot where I was exactly... Team Galactic are blocking a Lake, and I can't get to most other towns that I tried because a fat guy won't let me through... There's a Galactic warehouse but I need a key to get in the other rooms. I have no idea where this key is? I tried the ground next to the warehouse but maybe I'm just missing it. Help?