Accuracy is relative, would be better to have a specification (frequency, amplitude, phase, distortion). You can generate it analog or digitally. For digital generation, single chip DDS could be used.
An analog generator could be made from two integrators ("state variable filter/oscillator") and an amplitude stabilizer, directly producing 90° phase shifted quadrature components. Three-phase signal can be obtained from linear combination of quadrature components, or by phase shifter.
P.S.: Please delete your manifold cross-postings