Lyman,
This setup is no longer available. It's a Jones/Laurent, built in Canada. Paul Oerth also put some handlebar-mounted counters together for awhile, but I don't think you can get any from him anymore either. (I have one of the Paul Oerth versions as well, but the gear mechanism was very poor quality and couldn't be used.) The design was approved for measuring and I treasure this one and rue the day that it finally fails. It uses a flexible speedometer cable (like the ones used on old bike speedometers) between the gears at the axle and the counter. As I understand it, the design/production was abandoned because the cables became unavailable.
Ron