The following is a list of some ways to get free sunstones:
1. From the Daily Bonus Calendar when you log-in.
2. From Level Up Rewards when you level up.
3. From the Achievement House. Reach level 5, or the gold level, to get a sunstone from each mastery.
4. From Treasure Chests in the Mine (unlocked at level 30).
5. From contests on the Happy Acres Fanpage: https://www.facebook.com/playhappyacres
6. From the Lucky Wheel, which changes prizes randomly each day.
7. From playing events and reaching Sunstone rewards.
8. From random Treasure Chests on the Treasure Map.
9. From random Balloon Gifts collected on your farm or your Neighbors’ farms.
10. From playing with random Growth Decorations on your Neighbors' farms.
11. From Facebook Neighbors and Community Neighbors who send Sunstones as gifts.
Hope this helps!