Anything that’s rated for outdoor use should suffice. Qolsys doesn’t make a 319.5 S-Line outdoor sensor but DSC makes a PowerG one, the PG9314. Unfortunately, it is the only one we carry.
This guide here covers all of the tested compatible sensors from Qolsys directly
However, you may be able to find an outdoor contact on 319.5MHz elsewhere online.
In almost all cases however, the Outdoor contacts are larger in size and more expensive than their indoor counterparts.