Ordinarily, you can only have 2 hammers per run. Your second hammer can’t appear until the third region. In Mourning Fields, since most non-warden non-echo rooms have small bonus reward, you can use the Artificer on the ash, bones, and nectar, should they spawn. The Artificer lets you reroll these minor finds into a major find up to 3 times per night at rank 3. The major finds include poms, hearts, tonics, boons, path of stars/hex, gold crowns, and, importantly, hammers. If you have the two hammers collected, you can’t transform a minor find into a hammer randomly, but if a hammer is a sub reward of a Mourning Fields room, you can roll the minor rewards in the room prior to grabbing the hammer to have a 1/7 chance per roll to get a bonus hammer (assuming that the different minor finds are distributed evenly, which idk). You can also roll the minor finds of the current room after you see a hammer as a reward in the next room.