Speedometer Gear for Km?

You want the speedo to read in KPH? Take whatever the correct number of teeth was for MPH, and just divide by 1.609 to get the right gear for KPH. Example: 32 tooth now, change it to a 20 tooth. (Which would be great, but I believe the smallest gear they ever made had 21 teeth. Plus, has anyone ever seen a speedometer gear housing marked for smaller than 24 teeth?)
I think you'd be better off either getting a metric speedometer, or get a speedometer calibration gear box that attaches to the cable.