We demonstrate a broadly and continuously tunable optical parametric oscillator (OPO) based on orientation-patterned GaAs (OP-GaAs) operating at 2 kHz repetition rate. With the choice of the pump wavelength near λ = 3 µm, we were able to achieve tunable output in the whole range of 4-14.2 µm with a linewidth between 2 and 6 cm(-1), using a single OP-GaAs structure with a domain reversal period of 150 µm. The OPO output was tuned using (i) an intracavity diffraction grating, and (ii) fine adjustment of the pump wavelength near 3 µm. In certain portions of the spectrum this system potentially allows fast (sub-millisecond scale) wavelength tuning over > 2500 nm by fast steering the diffraction grating at a fixed pump wavelength.