I'm not sure what your plans are- ie do it yourself or looking for a gunsmith to do the work but I have had good service from Jerry at Mystic Precision. He carries all sorts of stuff including barrels and the guys he deals with (Mcgowan and Shilen I think) might have that reamer. There are a couple of custom barrel guys on Canadiangunnutz you could check out. I tried to shop Canadian barrel makers like Ron Smith and Ted Gaillard but the wait was too long for me.
You can generally easily get the button rifled barrels which are lapped. Cut rifled as far as I know no one in Canada is lapping them (to much extra time and cost). Rock Creek, Krieger and Barlein are usa makers which lap their barrels.
I thought Ted Gaillard started making 20 cals. If you need a barrel soon, drop me a pm I think I can help you there.
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