For clutch and rollers, try Dr. Pulley - better launch and higher top end.
I have used Dr. Pulley on my MP3 Piaggio as well as my Maxxer 250 with great results.
http://www.unionmaterial.com/rollerweight6.htmAs to clutch, unless there is something wrong with it, there is little reason to change it - it doesn't give you any performance benefit.
Tuning it is another matter - to either increase revs before take-up or to speed up 'grab'. You can do it with the stock clutch by playing with the springs, but if you must change it, again, Dr. Pulley makes a decent aftermarket tunable clutch for the Kymco.