Hi,
If it's helpful, I was able to calculate the numbers relatively accurately in the UK thanks to our fixed build number (450) and our 'Howmanyleft' platform that tells us how many cars are registered on the road, or SORN (Statutory Off Road Notification). In the UK a car must legally be one, or the other.
Here's the numbers I worked up, which may be a useful proxy to help you calculate the US number:
note: a small number of 1Ms are mislabelled by the DVLA as 135is so don't show up on this chart, but it's a small number
From this, a couple of things are clear:
1. The total (Registered + SORN) is shrinking, so they continue to be crashed/written off, lost or exported to other RHD markets.
2. LOTS are being SORNed. That means people are speculating. This is almost certainly the ultra-low mileage / mint / unmodded cars.
3. The number of regularly used ones is shrinking fast.
4. At current trends, in 5 years time, there'll be half as many as now on the roads.
Here's my maths:
Of the original 450:
93 (or 21%) are dead, exported or lost
126 (or 28%) are locked away by speculators to re-appear for crazy money in the future, or remain in long-term collections as an asset
231 (or 51%) are in use
Using those stats, mine is an Alpine white car, of which there were 150 of the 450 originally. If only roughly half are in use then that's 75 cars. So mine in effectively 1/75. In 5 years time that's 1/37.