I don't know the specifics of that car, so I'm going to take a stab and assume we're talking about coil springs.
Springs only squeak where they contact something else, which is why spraying them didn't help. If you can't see anything else in contact with the spring have a look at the top and bottom seats. Those seats sometimes wear. Not necessarily all the way through but enough to make the part where the spring sits uneven, resulting in movement.
Sometimes if the suspension has been worked on for any reason the springs and seats may not have been quite correctly matched up when it was put together, again resulting in movement. That movement causes squeaks.