Andy,
In addition to floyd's comments... this might be useful information.
If you locate the audio file for your selected Realdrums (it will be under bb\Drums), load the wma file into a DAW and scroll to the very end. The last couple of minutes of each Realdrum audio track contains a recording of each sound that the kit consists of. This will allow you to easily isolate the side-stick sound you are after.
Regards,
Noel