To unlock the events necessary to unlock the Maserati Ghibli you must find the Plymouth Roadrunner Barn Find and go back to the Garage.
I was trying to save the Roadrunner achievement for last but after doing everything (all Speed Cameras triggered, Roads discovered, Bucket Lists completed and Rewards Boards smashed) except racing people on the street between events, the Maserati Ghibli events would not pop up.
After I found the Roadrunner here:
Solution for Got nothin' but time In Forza Horizon 2 Presents Fast & Furious (Xbox 360)I went back to the Garage and took it out for a spin & when I did Tej told me that he found the Ghibli.
There are 3 events you need to beat to unlock the achievement:Fist Full of V8: a 3 Lap Circuit race around the streets of Nice. You unlock the Maserati Ghibli after winning this race.
Italian Triple: a Speed Combo race to hit the speed target across 3 Speed Traps
Fast or Furious: a Road Trip back to the Garage in double quick time
Now drive back & enter the Garage, the achievement is yours!