The BPA GG model is a simplified hydro gov model that has limited parameters as shown in the documentation of PowerWorld. There is nothing identical to it in PSSE, but since it is just two lead-lags, two integrators and one limiter, you could get a similar (but not identical) behaviour by using more advanced hydro governor models and then using the values of 0, 1 and 99 to bypass other models as needed(e.g., 1 for gains, 99 for limits and 0 for time constants and gains that needs eliminating).
You can try the WSHYGP model (WECC GP Hydro Governor Plus Turbine) as it has enough components, but at the same time not too complex. However, the only thing missing is that it starts with an integrator, rather than a lead-lag