N6129B is taken. It's currently assigned to a Talos Drones T60X registered in Mc Cune, KS.
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.
N6129B has been worn before. Past registrations from FAA deregistration records:
Tails one nudge away from N6129B that aren't assigned or reserved: