Alex Jupe motorsport do the quikshift, but it's not a kit, they rebuild the isostatic linkage as a custom fit onto your car. Otherwise, if it's particularly sloppy, renewing the pivot bush at the bottom of the shifter, under the car may well be a good improvement. For the DIY approach, check out some of Junglejustice's solutions on his 3.7 race car project (quite a few pages to check out, but well worth reading through the whole build IMHO) It involves a bit of cutting / welding to change the leverage rate of the shifter for a shorter throw. Some people have also simply shortened the shifter (take off the shift knob, cut the shaft down a bit and re-thread for the knob to go back on) for a similar effect of shortening the shifter throw, but of course this also puts the shift knob further from your hand when driving.
Performatek also do a kit called the 'monkey shifter' which is to renew the linkage but is not a quick shift type kit as such