The burrs themselves have been listed on the Mazzer site but not yet for sale as far as I know. I’m guessing but perhaps they’ll wait for the Philos to be available around the world first.
I’m not saying Mazzer are unique or special in this regard but I do like that the Philos and burrs have been designed to work together, in a world where grinder and burr are increasingly interchangeable.
Similarly to how Apple (queue the ‘I hate Apple’ comments…) have historically sandboxed their ecosystem to ensure things work well together.
I think people have tried other burrs in the Philos but not yet Philos burrs in other grinders. It’ll happen at some point.