I wouldn't have thought that buying a kit with a pre-made insert would be worth it?
By the time you have found someone with a lathe big enough to swing a whole wheel and also make the necessary jigs to hold it perfectly central, I'm sure they would be more than capable of making the insert.
I think it would also be better to machine the inner diameter, (the one that the bearing must fit into) after the insert was seized in with a good interference fit. It's all too easy to distort the insert when fitting and far more engineering sense to machine it perfectly concentric and round after it's fitted.
The first step is measure carefully exactly how much gap you need to overcome and any ovality. I'm sure you'll find that it's well within the scope of what the bearing fit jollop will do.
Wheel bearings should do tens of thousands of miles, so the next bearing change is most likely a problem for the next bloke..
