they're made by B&M, who make the original GS mirrors for BMW (or so I'm told). I got them from MPS (I think - a catalogue that came bundled with Bike or Ride one month - has a picture of a GSXR taken from above on the cover ).
They are excellent mirrors - but are a pain to fit. They have a wider thread than the standard ones. I overcame this by getting a engineering shop to cut the threaded studs off, drill the base and insert a threaded stud of the correct diameter - the job cost £20, but someone could probably do it cheaper if they had the tools & time...