Like the pimp master said go to
https://sdp-si.com/eStore/ go to metric then gears then spur gears. On the right hand screen drop down the bore size box and choose 6MM then drop down the Module box and choose 1. Go to the hub style and choose the one with set screw and it will give good carbon steel options of 12T (A 1C 8MYK10012), 14T (A 1C 8MYK10014), 15T (A 1C 8MYK10015), 18T (A 1C 8MYK10018) and 20T (A 1C 8MYK10020H).