yes them all
but only between day 694 to 700
I will writhe when I have more informations
Ore when i get the black race cars
but just remember that you need at least 8.299.996 to buy them (and i think the best way to do it is to buy then all at once)
(you can get the money easy in the money lap: look at Super cheats - Gran Turismo 4 - cheats/user submitted cheats and then find a cheat named Money lap ore easy money i think)
hope that helped ;)