I'm in Australia so I doubt where is useful to you but it was an engineering place in Brisbane, he was very reasonable too.
Once you have your shafts measure carefully the length shaft you want and if that cuts off all of the current spline your looking good then compare the ODs
I was originally thinking along the same lines of getting them cut and welded up but he suggested this way, I'm he did because it's a stronger, neater, and probably cheaper solution.
Looking at an on line video and there is specialized equipment for cutting splines so maybe look for someone who has that machine.