SAW Filter input power restriction
Basically you don't use a SAW filter at those power levels (They are a tool for receivers and power levels generally lower then 10dBm. 

915MHz is high enough that printing some sort of interdigital filter right on the board may work, or print the inductors and use lumped element caps? If you want really sharp skirts cavity designs are possible but can be a bit of a manufacturing pain.

You might find something off the shelf from someone like minicircuits, but usually this sort of thing is just something you design in one of the standard LC topologies, or as a microwave filter.