Hi there, have just registered to say this incase it helps, as I've just had to find this car for the 2nd time (let it go after spending days waiting for it to spawn, then decided I wanted it again.)
What works for me is to turn the PS3 off and then back on again. Reloading a save without doing this doesn't seem to really change much at all. Then, instead of just one or two cars changing here and there, there's a big change from the second the game starts again. Once I realized this I found one after a few attempts. Just to add though : I don't play online, not even connected, so not sure how that changes things, and I have a really old PS3, one of the first ones.
If those things don't make a big difference to car spawning though, I'd suggest going to the golf course car park, then simply save and turn the PS3 on and off a few times, and you should eventually see it right next to you when you get back into the game. Actually, knowing the way car spawning is messed up it could take more than a few times. It might take a short while, but it should definitely get you the car eventually without you having to do anything other than just turning the PS3 on and off for as many times as it takes to make the game spawn the car.