It must be something wrong with my cars.com search, compared to what's been seen here in this thread before - but I just searched, and got these numbers now...
Cars.com - 400
Carguru - 411
Autotrader - 426
TheParking EU - 583
For the Carguru and Autotrader sites - I selected nationwide (US) and for Cars.com I selected "all". The Parking I selected cars within the EU.