Interestingly enough, George Washington never wore a wig and Jefferson only did some of the time. Both of them pomaded, powdered, and styled their own hair. Haircare of the 18th century includes pomading and powder just like we use conditioner and shampoo today. So, if they were to go without their wigs they likely had their hair cut very short or would have had their hair styled just as the wigs. Since the only surviving images we have of these gentlemen are portraits, no one would sit for their portrait in a state of unfinished dress, so there would be little chance any surviving images of the time that show them without properly styled hair, be it their own or a wig. You can find some images of men in that time at the barber or in satires showing a bare head, but they aren't often of a particular person (some comedic satires here and there making fun of someone famous). There might be modern photoshopped images out there, but I can't really help with that.