Design for an analogue oscillator that doesn't drift in frequency?
Analog oscillators are going to drift.  For your purposes, a crystal is exact enough.  You can try to tweak a analog oscillator using something derived from a crystal as a reference.  But if you have the crystal there already, you might as well use it to make the desired frequencies directly.

Even a low end DSP clocked from a crystal can synthesize audio sine waves.  It can even digitally produce each of the sines internally, then add them to make a composite output signal.  This can be various harmonics with their own gains and phase shifts, or even arbitrary frequencies.  There is a reason you don't see analog synthesizers anymore.

I go into detail about how to generate sine waves inside a processor in this answer.