one method to get boron, is to buy a Shure V15 body, and a NEW Jico SAS on Boron
It comes with the brush you can use up or down like the Shure originals, however, Shure's brushes were/are damped, Jico's is non-damped.
And, you can have VAS rebuild you a frankencartridge, I've got an advanced stylus Steve calls 'P', on boron, with Shure's OEM damped brush that I can use in either my 97x body or V15Vx body