Available as an assembled Module and as a DIY project.
This Module is currently available.
Quadrature Oscillator
Low frequency to audio rate quadrature oscillator, outputting 4 sinewaves 90 degrees apart.
Based around two self-oscillating filter, it features a buffered frequency modulation input with attenuverter, a switch to cover 3 frequency ranges and fine tuning.
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These merchants probably sell this module. Huh?
Syntonie VU006 Quadrature Oscillator