What direct burial cable for alarm keybus in outbuilding?

I'm adding alarm to an outbuilding and can't find a good cable for running the system. I need four conductor direct burial cable. All I can find in four conductor cable is sold as speaker wire - it's straight through cable rather than twisted pair. Normal alarm wire, and the DSC spec, calls for twisted pair.

What cable do alarm pros use for running in buried pvc conduit to outbuildings?