Honda Reacon Shifter with 12mm made for Son

I'm New and was hoping I could get some assistance. My son 13 bought on his own a used Quad Honda Reacon ES 250. We did a father-son project of rebuilding the top end. The issue with the ES model is it doesn't have the standard STAR shape fitting for a foot gear shift. It has a 12mm and Honda doesn't make a foot shifter to fit these. I'm looking for someone that could make a shifter that will fit the 12mm fitting and be able to tighten it like a standard shifter clamp.

Thanks for any help you can give us.