Although there is one, length of spokes offered on the Sondors.com parts list page, they are Awfully Expensive. There might be Google results by searching "Sondors Original Spokes for Sale". . If you have the Sondors Rim, take it and the Hub (motor) to the best local bike shop and have them use their spoke calculator chart and cross check that spoke length against what you calculate on this online resource. Sondors Original Fat Wheels use a 2 cross pattern.
After you have the spokes 14g, nipples, spoke prep or linseed oil and your spoke wrench. You’ll need a Parks Pro Wheel Truing Stand.