Most of the free sites with MLS access have very limited capability. They are not nearly as powerful or versatile as the direct access the Realtors have. Your best bet is to contact any Realtor and they can set you up with automatic notifications based on your criteria, including properties with contingencies.
BTW, why are you interested in properties with contingencies? They not necessarily represent a good value (might or might not) and a good percentage of them close and never become available.