Speedometer Head Repair

I am from Ohio. I have a 1971 Demon 340 equipped with the rallye dash. I need to get an odometer repaired. It goes from 86,590, 86,591 and up and when it gets to 86,599, it goes back to 86,590. The speedometer works fine. Who can I take the speedometer head to and get it repaired? Thank you all in advance for your help.