None of the solutions appear to to have any current working methods of getting this achievement.
How can I unlock this now that the Forza 3 VIP and DLC is all delisted?
There are no more unicorns given out through events, the forzarewards program, auction house, etc.
I think this is now partially discontinued now that Forza 3 vip/dlc is all gone, which was
used for importing into Forza 4 to get unicorn achievement.