Henry Rempel should be able to do this for you, as can ATRS, Calgary Shooting Center, Badlands.
KGL
E mailed a few places, 125$ seems to be the standard, but no one seems to offer a Matte black one without getting it cerakoted
I used to get them done, any competent gunsmith can do it. Now I just use the KRG bolt knobs, I especially like their newer and smaller SV version.




























