Hi Stephen,

Let me start by saying that it will not be easy, but it is very well possible to read the exact frequency of a radio.

You need to locate the LO (Local Oscillator) in your tuner. This is the generator that creates the mixing frequency.
Depending on the frequency range you may need a prescaler to divide this frequency by 16 .... 512 or whatever is approriate.
The most difficult part is to couple the oscillator with the prescaler. Especialy to couple it without mistuning the oscillator. Sorry I can't help you with that because of the diversity of tuners.
But if you did manage to couple the prescaler you can measure it's output frequency with an 8051. There must be plenty examples of code available on the net to do that.
If you know the frequency of the oscillator you can calculate the exact frequency the tuner is set to. Multiply the measured frequency by the prescaler value (so if the prescaler diveded by 16, you'll have to multiply with 16 again). Then subtract the IF frequency from this value and you have the frequency you're looking for. If you read a frequency that is too far off of what you expect you may have to change the subtract function into an add function.
If you don't know what the IF frequency is you may find it printed on one of the filters inside your tuner. AM tuners use IF frequencies of approx. 450kHz. FM tuners use 10.7MHz. But other values may exist too.

Good luck