Latest (free) DLC in GT Sport added Monza and a bunch new cars.
Here's a close up of the two 20 million credit ones:
Ferrari P330 P3 on Monza
Jaguar XJ13 on Big Willow
That took a bit of grinding and selling all my saved up cars. 20 million is still the max credits you can have, now back to zero.
This car was fun to use as well Toyota 2000gt on the Nordschleife, does not end well.