Where to get a boar knot

Get an Omega brush from Connaught removing knot is one option but with knot placed in black plastic cup for example a 27 mm knot needs a 31 or maybe 32 mm hole in new handle.
This is something that I need to figure out before I order the knots. My brush currently has a 24mm knot and I thought a new 24mm knot would fit..... I guess it's a bit more complicated :)