What kind of stem are you using? I use alot of Kalloy hybrid type stems that have alot of height to them.
I recently had the steerer tube extended on two forks, the guy doing the job simply cut the old steerer off and welded on a new steerer.
Have you considered a threadless adapter and a threadless type stem?
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk