Deadstang,
There are around 900 in the registry (that may go up with new "finds" that come out in the next registry), but as statistics show cars over 30 years old there is usually around 50% still remaining. Now that means in any conditions, from concourse to hunks of metal in a junk yard. The other 50% is beleived to have been destroyed through crashes or junk yards. As for the number actually on the road, if you go with what is in the registry it would be around 900 but remember that is only those that are known about. I have been working on purchasing a car that has been sitting for over 15 years and the owner does not know anything about the car. So they are still out there!
I don't know if that answers your question but I do know that there are over 300 on the road. You may have read about the HCS, there where only 250 made in 68 and I would assume that the number still on the road is around 150.
Doug