find a shimano 105 or simular LOW stack headset and measure total size
without cups(you know what i mean) then measure yours probably a king etc,should find about 5mm
If you know someone with a press, you can get the steerer pressed out and a new one pressed in...(rst have the same steerer dimentions at the crown).
We did this with my old mag 21's about 8 years ago and theres never been a problem.
It was done with a manual press with little pressure and no damage was done to either the steerer (which was used on another bike) or the crown.
Ive heard that the steerers are pressed in under 100s of tonnes of pressure.....well it sure didnt take that much to get it out or the new one back in.