N4426Z is taken. It's currently assigned to a 1997 Pzl-Swidnik PW-5 registered in Spring, TX.
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.
N4426Z has been worn before. Past registrations from FAA deregistration records:
Tails one nudge away from N4426Z that aren't assigned or reserved: