I use sdp-si.com for my chain drive. I'm currently using the #25 size ones. This is a link to the sprocket section https://sdp-si.com/eStore/CoverPg/Drive_Components.htm you'll want to get a hub sprocket for the motor. Use the metric if you want to find an 8mm bore size. Also the Metric and imperial #25's can be used interchangeably.