There is a Sky Resources guide that should get you from any island to sapling and dirt, then the better questing book takes over. Search controls for the Sky Resources guide hotkey, make sure it doesn't conflict with anything.
Once you get your first black petal you can plant it in grass or dirt, then bonemeal to grow a tall flower, then shear that to get it as an item. You can turn tall flower items into 4 petals. Net gain is 3 petals. You can repeat this process as needed to 4x your petals (or flowers) each time.