I haven't seen anything about this online so I'm probably the first one to post it. It was shown to me by a friend.
Go to the location marked on the map (link below). There will be a small scrap yard, go inside you should see either : A red Peyote, Purple Manana, Green Buccaneer, OR 2 of these cars side by side. The Peyote and Buccaneer have a Matte Pearlescent paint job which looks great. They already have some mods on them too. The time doesn't seem to matter too much but day time seems to be best for spawns.
The Manana has no roof, neither does the Peyote. You're welcome!
Click that, then click the icon to show the map location. When I went there to take that photo for this post, the Manana was there so that just shows how easy it is to get it to spawn. Sometimes there will be nothing, sometimes there will be 2 cars there, but you won't have to try for long before you get what you want.
Here's a pic of my own one with the spawned one.
EDIT: Literally just after I posted this I went to Grove Street, and there was a purple Manana there at 12:45pm clear weather.
EDIT again: 2 mins later saw a green one on Strawberry. pretty sure this is because I was driving a Manana because I've never seen one spawn online there before, and if they do it's rare.
EDIT 3: Convertible Tornado also spawns at the above location. Looks amazing in my crew colour! (SURF)