The 4 cars are Juan’s 1956 Beaumont Valentina, 1985 Tokai Sabuku, Yami’s 2008 Kag TG and 1962 Verrazzano Bravo.
Juan’s car can be earned by completing the mission “Fuel the revolution”. It is an early game story mission so you will likely already have this one unlocked.
The Tokai Subaku can be found in a warehouse at the FND Storage Facility in Catalina Ridge, La Joya, El Este. It is the restricted area south east of the CCE Electrical Station 31 military base and north of the La Joya Chemical Plant. Upon arriving, head to the back of the large warehouse and climb up the digger. Jump up it’s arm and jump into the open door on the side of the warehouse. Break the pallet to your right and crouch under the boxes. Jump over the box to your right and walk around. Break the boxes in front of you and jump over again. Slide under the shelf and box and you should find yourself at the top of a staircase. Walk down the stairs and get in the car then drive it out and after a few seconds, it should pop up as a new ride.
Yami’s car can be obtained by completing the Yaran Story “Backseat Driver” at Yami’s Chop Shop. It is located in Madrugada, north west of Montero Farm, the main base for this region. It is on the bend below the Colinas Plains sign on the map. You will then have to secure the FND Tank Training Ground up in the Oasis Plains region of Aguas Lindas. Oddly enough, I didn’t have to fight any tanks, just four jeeps with gunners which was easy enough. Once you have killed all the soldiers, you will be teleported to the car. Get in, drive out of the training ground and after a short phone call with Yami, she will tell you to keep it. Within a few seconds, the car should pop up as a new ride.
You can get the Verrazzano Bravo simply by completing any Gran Premio race. They are time trials and you should find you have plenty of time to complete them. After finishing one, the Verrazzano should pop up as a new ride.
You should now have all the rides and the achievement. I have linked some helpful guides below. Happy hunting :)
All ride locations (By PowerPyx)
All Gran Premio races (By PowerPyx)
https://www.powerpyx.com/far-cry-6-all-gran-premio-race-loca...