Park Tool TNS-1 Threadless Nut Setter
The Threadless Nut Setter is used to install the star flanged nut found on 1" and 1-1/8" threadless headset systems. Thread the nut onto the TNS, insert into the fork stack, and tap it in with a hammer. Sets the star flanged nut to 15mm and keeps it straight. Long handle helps prevent pinched fingers.
Note: Star nuts not included
Could be cheaper for what it is but does the trick. Helps if you use a stem or tube to help align this with the steer tube and keep things straight.