I dunno if someone has already posted this, but I know a lot of people are asking where to find it.
Well I'm pretty sure I've found a permanent spawn point for the car.
If you find the arch in the circle in Broker (in the Outlook neighbourhood) on the North side of this arch is a small restaurant called 'Pizza Salad'. (you can't miss it, it's on the main road northbound). It's basically parked outside that restaurant on the road next to the outdoor seating.
I've seen it everytime I've passed by there recently in any car, and it's always a yellow infernus.
I'm not sure what's activated this though, but I'm personally at 98.33% completion.
This is where the guide says it spawns. However every time I go there its never there, I must have tried about 20 times and it wasn't there, and been past there just cruising a decent 10-15 times, and I'm pretty sure it wasn't there then either.
I delivered the Infernus for Stevie ages ago and have not seen it there once since. Also I'm sure somebody else would have mentioned it before if it constantly spwans there after it's been delivered. Think it was gold as well.
Maybe once someone completes all of Stevie's requested cars some of those cars become there permanent spawnpoints , the cars varrying from game to game. Because some people also see the Comet near the golf place all the time as well.