Some of the clutch parts are still available from your local Kawasaki dealer. I'm not sure about that specific bushing (I don't have my parts manual near by to look it up), but looks like those plastic sliders are re-numbered and still available. Here's some info from the parts interchange thread:
Renumbered Kawasaki Parts that are still available from a dealer:
Pin 6.5x10x38 old pn# 920243-3001, new pn# 92043-1370
Bushing 40x44x12 old pn# 92028-3008, new pn# 92028-1511
Spacer 10x16x.8 old pn# 92026-3001, new pn# 92026-1304
Nut, special lock 6mm pn# 92019-008, still available under same part number
Roller old pn# 92122-3001, new pn# 92122-1152
Washer, spider old pn# 92022-3016, new pn# 92022-1899
Bolt, flanged 6x20 old pn# 92001-3001, new pn# 92150-1014
Bushing 32x36x20 old pn# 92028-3005, new pn# 92028-1513
Bushing 25x28x30 old pn# 92028-3004, new pn# 92028-1514
Bushing 50x55x20 old pn# 92028-3006, new pn# 92028-1512
Washer Split old pn# 92022-3001, new pn# 92022-1897
Washer, special conical old pn# 92022-3015, new pn# 92022-1901
Guide, Wear (plastic clutch guides 79-82) old pn# 13070-3002 new pn# 13070-1185