From the picture it appears the camera has a protection glass element in front, which is what's broken.
If this is true, then you can definitely replace it with a piece of plexi (or polycarbonate) because it plays no optical role (just protection).
Alternatively, measure out the diameter in mm and then google for a UV filter as close to that size as humanly possible (within 1mm preferably). Buy that UV filter, then apply a 3M clear film on top and then glue it to the front of the camera with clear silicone or some marine glue/sealant.
Just a few ideas for you...
2009 E90 M3 ED
2014 X1 28i ED