You can't trade stealth cars.
To get stealth cars, you put in a code right? The code brought you to PSN store and made you download the stealth cars, right? So you should be able to go to the PSN store and go to purchased. You should be able to download your cars again.
Do you still have your password 'n username for your old PSN? You can still log-in and go to purchasedI can probably find the old code, but its probably attached to my old PSN account. This is why I'm starting all over....ugh. Thanks guys, I'll work on finding that old code in my email.
Even if you find the code you wont be able to use it, is will say the code have already been used. what you can do tho is to create a 2'nd account on your ps3, with the acconut where you first entered the code on. Go to ps store and download them again, you wont need the code, they'll be there anyway. as long as you dont delete that account, your 2'nd account will get the cars aswell.