The M Performance brakes are extremely uncommon for our G30 cars and all BMW's in general. I'm not sure there's a way to get an accurate number because the people I've seen get them- 2 here on the forum) have got them aftermarket or after they had their car for a period of time so there's really no way of getting accurate statistics.
I'd say 0.1% isn't a bad guess.
The M Sport Brakes on the other hand are more common and a little easier to accurately track.
According to BMWVinCheck.com (a fellow forum member made this website where you can compare your cars options with other BMWs), shows M Sport Brakes are equipped on 4% of 530i vehicles and on 11% of 540i vehicles in the US (similar results outside the US). And then for all BMWs in general, M Sport Brakes are equipped on just 1% of all BMWs they have data for which equates to only 362 out of 39,897 BMWs.
The only caveat to that is the rather small data pool they have collected data on. It's a relatively new website I believe and they only have data on about 200 G30 vehicles so while it doesn't give concrete statistics, it's a solid tool to glance at and cool website nonetheless.
https://www.bmwvincheck.com
@Pupsaiden is the member who made the website. He's always looking for feedback and open for ways to improve his site. Big shout out to him.