Figure out what spoke length you need and go to
http://holmeshobbies.com/Sapim-Stainless-Custom-Spokes.html and place yer order fer the spokes ya need. I have a Catrike Expedition with a Cargo Monster extension. The motor is a beast C'lyte 3540, hooked to a Lyens 18 FET low RDS controller, programmed for 5000W and there is a 72V 32AH Turnigy LiPo battery to run it all. I put 12 gauge Sapim spokes from Holmes on it and have thoroughly thumped that trike and the spokes are still in fine shape two years on.
Here she is with just the GM Pro 901 motor.
I used 13 gauge spokes with the Golden Motor and hit some pretty high speeds. No issues at all. After adding the extension, fairing etc., the combined weight of the trike and myself is over 300 lbs. So it has 12 gauge spokes now.
As always YMMV