For parts, first thing I do is check the diagrams at Partzilla, then search the full part number over on eebbaayy to see if NOS is available, either for purchase at reasonable cost or for a good photo to see what a new part looks like. Then I search the part by name & alternate moniker.
Z1Enterprises . com has maintenance & other stuff for the motorcycle. If you need to do wiring, they have colored wire which is kind of handy, so that you can try to keep things close to stock & similar to the wiring diagram.
A motorcycle salvage yard might have some stuff. There was a good one near me, but it closed down a couple of years ago.
1981 KZ650-CSR. Competition, Sports & Road.