Have a look at the Optisystem or optisimulation tool. Or else, you can incorporate simulation of SBS effect under the steady state. Pre- and post- threshold conditions have to be brought in the context of pump depletion. Have a look at this article.

Article An approximate analytic solution of the steady state Brillou...

you can use the bidirectional fiber in Optisystem tool which include the SBS effect. Have a look at this article

Simulation and experimental validation of gain saturation in raman fiber amplifier