In my personal experience regarding Supercars in GTAV...
Common tier for me, seen multiple times around the map:
Infernus, 9F, Adder (at spawn), Banshee, Bullet GT, Carbonizzare, Comet, Cognoscenti Cabrio, Coquette, Ocelot F620, Feltzer, Coil Voltic, Surano, Rapid GT
Thanks to GTA's typical car-spawning mechanic you'll start seeing these cars more and more often if you drive one, tune up one and save one in your garage. I never saw a coil voltic in my save until like 100 hours of gameplay, then took it to a shop and suddenly, they're everywhere even if it's parked in my garage, this oughta work for all others too.
Vacca is a special case, has a fixed spawn near Franklins house but seems to disappear after the Epsilon mission.
Never ever seen a Karin Futo in singleplayer (they're everywhere on online). Heard they can be found in Rockford Hills area, currently 8 hours seeking and counting.
Never seen Entity XF or Cheetah anywhere. The Khamelion electric supercar is for special edition only and only for Online.
And then I don't know jack sh*t about the vintage cars My current favourite is the Carbonizzare because of it's oh so lovely engine yowling
Edit, to reply to the poster above me.
"No realistic driving but exagerate car/player damage in crashes."
Dude what are you smoking, the cars in this game are way toughter than in real life, the damage that the cars take is nothing compared to an actual crash
Edited by Perplex, 17 October 2013 - 06:46 PM.