Mine is manually tuned, but I suppose it could be modded for a microcontroller. I will post it anyway, it uses a varactor-potentiometer combo for tuner.
Closest thing I can think of to what you want is TDA 7084, it has push button tuning, continues to step up voltage feedback untill it locks, kind of like the many cheap walkman's that have push-button tuning. I'm not sure that qualifies as 'electronic' tuning, though. TDA 7000's series are simple superhet chips that use a very low frequency IF stage. Circuit I have uses the NE 602/AN 602 for mixer, then a PLL chip. I can't remember the # for PLL chip, but I have the chip. Probably you could look up the data sheet spec's for it.
Probably you could get ahold of a manufacturer's schematic for a commercial one. I'll look around and post back later.