Play the dream car championship, save it after completing race six (you will notice you can save the game during a series). Then start race seven (you dont need to even complete the race) and exit from the start of the race, don't retire though just exit. You will have won the series if you placed pretty good through the first six races. Chances are it will give you the wrong car the first time around (but you can reload and quit out again until you get the F090/S). This is exactly how I got it, it took me about 5 reloads. Hopefully you have a good car to race this series though.