Generating 19kHz and 38kHz phase-locked sine waves
Generate a sawtooth wave (so it has even harmonics) at 19kHz and use a 19kHz and 38kHz tank circuits to get the two frequencies. Or take the 19kHz sine and rectify it (full wave rectification doubles the frequency).

Here's a stereo decoder from my Leak Troughline Stereo tuner (only 3 transistors):


Q1 amplifies the pilot tone, which is then rectified (using D3 and D4), then Q2 generates the 38kHz signal that is phase locked to the pilot tone.

Though I'm sure it's possible to do this easier now compared to when the FM stereo was just introduced (and the tuner was designed).