I am in Michigan so not too dissimilar to you in habitats. What I have found to be a sure fire bet is to find swampy woods or just some woods, they almost always have some vernal pools in them. Then start turning ANY logs near the water especially in higher ground. Don't give up youll find them! I find them almost daily all year long except for winter. If all else fails wait till about march to April and go to a vernal pool somewhere with your flashlight just after dark, you will most certainly see some migrating to their pools.
Best of luck and I hope you see some. They are really special little buddies!