You can get the power berries by:
1. When you are in winter, go by the winter mine,there would be a power berry on one of the floors.(I can't really remember the floor.)
2. There is another one right on top of the winter mine.Go behind it and talk to the cave.
3. After you buy all the products on the TV shopping channel, the last thing they would be selling is a power berry.
4. There is one when you win the dog competion.
5. There is one when you win the horse competion.
6. You can one from the Mayor with your medals at the horse competeion.
7. When you Tilt your land, you shhould get a power berry.
8. There is one inside the spring mine.(can't remember what floor it is)
9. When you give the harves goddess something for a couple of days, she should give you a power berry, then give one wish.
10. I can't remember where this one is.
Sorry that I can't help you with the 10th one and the one with the floors.
Thanks To Vault For The Cool Sig