These are harder to find then the good old rocking horse poo, #41700 is the number but other 34mm Mikuni carbies I'm sure will do the job.
I too was seeking this elusive animal a while back, my luck must have been with me that day because not only did i find a carby body, I also found a M airbox in mint condition. Now I have two airboxes, one for my S the other to suit an M.
I still need some of the internals like a #2.5CA slide with idle cut-out on left hand side and key slot opposite.