I’m not recommending Campy, just answering the question of what I’m using. I bought my Campy toolkit used in about Y2k when they were cheaper and more plentiful.
I only mention it in case anyone has access to a Campy handle but they want to build for 9/8" steerers: my toolkit came to me with the cutter for 1" but also in the box was a Silva-brand cutter for 9/8". The Silva looks so identical to the Campy that they must be made by the same shop. It fits perfectly on the Campy handle.
Torch & File (Andy Newlands) sells Silva stuff and may have that cutter or could get it for you. Again, that would only make $ sense if you already had the Campy handle. But the quality is godlike. Mine is Ti-nitride coated, not sure if they come like that or if it’s aftermarket. Supposed to make it more long-wearing, but as a hobbyist I’m not putting too much wear on cutters, uncoated would be fine.
I also made an arbor to chuck it in the lathe, but that’s another subject.
Edit:
Just found this, a Campy handle for only $50 on ebay.
You’d have to source or make all the other parts. Making the nut for that trapezoidal thread is probably beyond my machinist skillz, so hopefully that part can be bought somewhere. The cone is about the only other part you’d need beside the nut and the cutter, and would be easy to make for anyone with a lathe
Same seller has a complete handle with cutter and all the parts (even the go/no-go gauge) for $360. I’m not in touch with prices but that sounds decent.
EDIT#2:
Just noticed that ebay seller has two of the complete cutter set, at the same price, but the cutters are different.
One has the older style cutter that doesn’t make the 45° chamfer, which I think dates it to early '70s before the Super Record headset with alloy lower cup came out.
Here (below) is the other one they’re selling, check out those chamfer blades. What a cool cutter, more expensive to get it resharpened though I bet:
I think I see some wear on that cutter, so don’t assume it’s sharp.