If you’re looking for the wilwood aluminum hubs, they’re only available with 1/2”-20 studs.
UMI Performance uses these hubs with their C5/ C6 brake kit.
The rotors slide over the hubs and widen the track width .25” per side.
You can machine the rotor off your existing hubs to keep the M12 studs. The rotors still slide over the hubs and widen the track width the same .25” per side.
If all you need is 1/4”, maybe this would work, although I’m not sure what rotors you need for the calipers you have.