You might try these guys...
"I just had my speedometer repaired by Palo Alto Speedometer. I had taken my reset knob off when I sent it to them. They offered to supply me one for $10. As a matter of fact, I just put it back in the car a few hours ago.
They advertise in British Car, but you can reach them at 415-323-0243."
Note, this is from an old message I saved -- ISTR they have a new phone number.