You're confusing a couple of things here. Arm themselves sell Microprocessor core architectures and core layouts for putting in an IC. You need to have access to a chip factory and extensive tooling to take one of these cores, and make a microcontroller out of it.
Breadboard doesn't come into play anywhere there. You need to do this on a chip wafer. You can't even buy such a core implemented on an IC – it would be useless, because you need to add things like power distribution, RAM, and internal buses to it before it can function as a component.
It's physically impossible to even route enough signals for the buses internal to such a microcontroller on a breadboard. Also, breadboard has very bad electrical properties, so that this wouldn't work for a host of other problems, starting with the fact that you need to add strong drivers to your chip in order to even be able to drive the capacitive load a breadboard line is.