Minecraft wiki entry for Gathering_resources_on_peaceful_difficulty, associated text: There are 2 more ways to find bones. One of them is through fishing. If you fish with a fishing rod without a Luck of the Sea enchantment, you will have a 1.1% chance of getting a bone. However, the disadvantages of this method are that a fishing rod requires string, which is most commonly obtained from spiders, which don't spawn in Peaceful, and that you will only have a small chance of getting a bone when fishing.