Electronic – Do narrow-band single-chip bandpass filters for audio frequencies exist

Do digital Anti Aliasing filters exist for traditional ADCs?

Not in the sense you are discussing. There are other forms of "aliasing", but you seem to be considering only analog to digital conversion. If the signal is already digital (so that you can filter it digitally), then it's already been aliased. It's too late.

Where usually do people put these filters?. On the IC for the ADC itself?

I'm sure you can find ADCs with integrated filters, but it's not the norm. Different designs have different filtering requirements. You may need a linear phase filter, or you may not. You may need very good performance, or you may need very low cost. You might not even need filtering at all, if you know what frequencies your analog signal can contain.

Are physically big filters (e.g. through hole capacitors, inductors and resistors) the norm?

Not really, for reasons of cost. You need bigger components if you need to handle more power. High power is not usually something you need to drive an ADC. It may also be that a particular design requires a high capacitance or high inductance that's attainable only through large components, but a good engineer will avoid it if possible. Much better to use a 2 cent SMT capacitor, than a 20 cent through-hole electrolytic, wherever possible.

The main part of the filter (sectioned in red below) is a modified MFLP filter and not a Sallen-key filter: -

I've used Mr. Okawa's web site for doing the analysis and it tells me that the cut-off frequency is about 3.2kHz and there should be no peaking because the Q (or damping ratio if you did the math) is about optimum for flat response (\$\frac{1}{\sqrt2}\$).

The high pass stage is at the input with C1 and R2//R3. This works out at 318 Hz for it's 3dB point.

One slight modification to the general type of circuit is the 2nd op-amp (that forms the MFLP filter) receives mid-rail bias from R2 and R3 but also a smidgin' of input signal. This doesn't alter the frequency response too much but does subtract 1 from the calculated gain of the 2nd stage. Okawa calculated it at 10 when I believe, with the modification it will be 9. The first op-amp stage gain is 11 and the total gain (at mid-frequency) will be 99 and not 100!