This works as I have done it many times
If you know some one handy with a lathe and knows how to measure and use it!
they turn the seat down on the fork to almost the steerer, Example 25.6mm
Then turn a mild steel bush with ID of 25.50mm and OD of 26.7 -26.8 and part off about 6mm long
One presses the bush onto the fork (interference fit)
then the fork is returned to the lathe
and one takes very light cuts till you have 26.42 -26.44mm
Fit Camp 26.40m crown race
Works fine.