Brownalls carry the Ruger extractors. And in any event they would be very simple to file out from solid if needs be out of a piece of O2 or A2. I rebarreled mine to 6mm BR Norma from .300WM so had it apart a dozen times and changed the extractor. Yes there is a problem with cutting both at the same time in that the extractor is designed to move out of the way left horizontally for rimless cartridges so it would tend to move out of the way of the rim cut on the reamer. I think that you would have to wedge it in its contact position to the right when you machined the rim.

Regards