The conversion from miles to kilometres is not dependant on the changing number, threrefore the movement of the needle would not change, only the location where the needle meets 10,20,30 etc should change and different units will use different conversion ratio's.
Unless companies sell a dial kit giving both numbers it would be easy enough to design your own. If you have miles but want to include KM, you could calculate the number of degree's per mile and convert this into degree's for each KM. Making it look decent would be the issue, and printing it on a nice laminate... it could be done though
There must be dial kits out there somewhere showing both???