Hi Renthal are making the rear sprockets specific for the GSX-S, you can buy direct from them but I also see that AR Racing in the UK have them listed on EBay in 43,44,45,46 and 47 tooth options. I've bought from them before direct off their own web site and they were very helpful. I'm not at home so can't check what the standard front or rear tooth number is, but that range should be sufficient I hope. So that just leaves the question as to whether a gearbox sprocket that fits a k5 GSXR will fit the GSX-S, again hopefully that is the case and it's a simple job to order one with the number of teeth you want. I will stick to -1 front and plus 1 rear as top speed is irrelevant over here but I've found the lower gearing makes for more entertainment value....