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I tried a trick from model engineering, LBSC methods, in our shop last month. Our staybolts have a taper bore in each end (about 12 degrees total) to fit the expanding or swaging tool that expands the staybolts for a pressure tight fit.

Previously, my colleagues had dedicated a lathe to boring each taper with the topslide one at a time. I said, huh? Being lazy, I said, "why don't we have a reamer to do this?" They looked at me and said, "Yeah, right." (in Danish, sarcastically).

I said, "so, got any drill rod?" No, they did not. But digging around in the scrap, I found a really old, useless alignment punch. I annealed it. I turned it to the correct taper. I put it in the mill and shaved it down to a clean half round, taking care to maintain a sharp edge. I hardened it and tempered it (by sight, with a torch).

You could not go crazy, but it would cut with reasonable speed (and a good dose of olive oil, my favorite cutting oil). We processed 80 staybolts with this reamer before it failed, and then a second one I made cut 60 more, and is still sharp in the tool drawer.

Anyway, my point being, this might work if you are desperate or too cheap to buy the good reamer. Especially for a one time cut.

If you had a larger reamer that you don't think you'll use, you could cylindrical grind it to the correct diameter +.010 or so. Then if you have cutter grinder capabilities, you could grind the primary and secondary relief on it and have what you need. Then you could shop for the bigger one.