Hopefully this winds up getting stickied.
Let's compile a rare vehicle list and if you wish to reveal how you found it, that is up to you.
Ratloader i found by using an Intruder by the military base. They began to flow in and out one after another.
The Intruder i believe i was in an Elegy by the airport and Scrap Yard from death metal.
Felon GT i was in the Bullet next to my apartment (200k one by the beach)
Rancher (i think it's rare) i was in Paletto Bay in my Carbonizzare