Need one replacement spoke? Need a custom sized spokes for an odd wheel/hub combo? You could rummage around your motorcycle graveyard, order some online if you can find them, or you can do it yourself, the good ol' fashioned way.
Start out with solid rod the same diameter as your other spokes. You can use mild steel if you want to paint them, zinc plated or SS if you want to keep them bare and rust free, or Cro-Mo for light and strong (cro-mo mig/tig wire needed for welding cro-mo and SS wire for SS or the weld will fail). First thread the end. Most spoke nuts are 40 TPI. You might find yours to be different though.
Cut it to length leaving enough for the bend.
You can either heat and bend or just smack it over with the hammer if the gauge is small enough.
Check your angles.
I drilled and counter-sunk a hole in a 12ga. sheet of copper. You can also use brass.
Clamp in the spoke leaving the desired length out to weld the nipple on.
Lay your copper sheet on top with your spoke protruding with enough material to weld on.
Put a nice dab down. make sure you get the heat on the spoke to make good penetration. You dont want a cold joint here.
Grind and file the bead down til you are happy with it and it fits the dill-outs in the hub.
There you go, your hand made spoke.
Disclaimer: You are responsible for your own safety and the safety of others who ride your bike.