How do you get all the sun rocks in Harvest Moon?

You must give him five 300+ gifts. You can not give him the gifts all in one day. You must do them separately on five different days.

Some easy gifts to get are:

Bamboo Shoots, Blueberry, Chestnut, Egg, Fish any size, Chocolate, Milk, Corn, and Potatoes.

After that he will thank you for all the gifts you have given him by giving you a Sunstone in return.