N100 is taken. It's currently assigned to a 1940 Piper J3C-65 registered in Ketchum, OK.
See the full aircraft record →A tail number only frees up if the owner deregisters the aircraft or moves it to a different N-number — and even then the FAA holds it before releasing it to the public.
N100 has been worn before. Past registrations from FAA deregistration records: