OAK TOWN - day into evening
Canary Stage Eternal, Cheetah Stage**, Whale Stage**
** means you are warped away as soon as you reach the goal size, so you won't be able to get some large items.
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Those are the only levels that have oak town in them, I'm guessing. I haven't played MMK in forever but I would say start by playing those levels over and over again, eventually the new area has to pop up.
Edit: I just fired it up to check. There's three you can get, snow, dusk(which has an orange sky) and daytime.
I'm almost certain it's the one that's just daytime, no snow and a clear sky.

I know this doesn't help too much. Sorry the quality of the pic isn't that great, the psp isn't photogenic.