It's hard to build an oscillator

Never found it hard to build an oscillator, the hard part is musical voltage per octave. 3340 repro chips are the way to go, the best non-3340 circuit I've seen is this one and it's still temperature-sensitive: https://www.youtube.com/watch?v=FiCMjt0mqvI

Temperature sensitivity only matters in polysynths where you don't have easy access to per-oscillator tuning. It is not difficult to build an oscillator with better pitch stability than a guitar, even my VCOs with no temperature compensation require less tuning than any guitar I have owned.

But that's for synths where the oscillators are ICs. I'm talking about simple oscillators from basic components

My VCOs which lack temperature compensation are oscillators built from basic components. The closest I have to oscillator on an IC these days, are the VCOs in my Moog Prodigy which use a quad OPAmp and a 3086 transistor array, it is far more stable than any guitar string.

3340s are great. I've also heard good things about the SSI2130 and 2131 chips as a more modern alternative to 3340.

3340s are more DIY-friendly though, as they're DIP packages.