Is there a way of recovering car memory(radio,time) after forgetting to use a memory saver?
Usually not. When a component relies on volatile memory to store settings it's often because the manufacturer wanted to cut costs by not including permanent storage. Once the data's gone, it's gone for good.
The memory used to store the radio stations is volatile, and once the battery is removed, the data is gone.
May be, some radios have a power buffer to keep the data for a short period, or they have non-volatile memory. But in this case, the stations would just be there, and you don't have to recover them somehow.
For the clock, it's the same.