1) Go to the car collection menu and then continuously pressing Y and A over the Willys MB Jeep.
2) After around 10 seconds you'll have roughly 50 of them.
3) Exit out and go buy the super wheel spin in the skill tree (only costs 5 skill points)
4) Favourite the car you've already done it on so you don't get them confused
5) Gift drop your cars when your done so you get the 5 skill points refunded back to you
6) Repeat