Thanks for the tip. I emailed Gripsport and Jon Weaving emailed me back with a friendly and informative response about his service. I really like the way it's engineered and the cost of the service is very reasonable. Unfortunately I calculated a few shipping estimates and overseas shipping alone would cost me at least $200 (about 90 pounds) and up to $375 (170 pounds). By the time all was said and done, this fork would cost me no less than $530 or about 235 GBP.
It's disappointing really as I had engineered this technique up in my mind some time ago and when I called Dekerf (they're from Vancouver) to provide the service they said they couldn't do it for safety reasons.
However, now I'm really at a loss, since Dekerf informed me that the extension method isn't safe due to the heat necessary during the brazing process and Gripsport states that pressing out the original steerer isn't safe either.
Damnit! all for a lousy cm.
On the other hand, I'd love to find a early 90's 17.5" Rocky Mountain Blizzard or Altitude frame. This fork would be ideal as is for one of those.
96 Kona Ku
93 Rocky Mountain Blizzard
94 Rocky Mountain Altitude