I encounteed the OP's situation yesterday while trying to book SMF-PHL in L. I have found that I can often get around this by asking for a multi city itinerary on .bomb. Even though SMF-PHL was showing L0 alll day, I was able to book SMF-DEN then DEN-PHL in L. It helps to be as specific as possible in your search request. Let's say you know in advance that your desired fare bucket is available from A to B and then from B to C for a particular date/time/flight. Rather than pricing as two individual segments A-B plus B-C, united.com will generally give you the A-C price. This happens even if A-C is showing zero availability in your fare bucket, assuming you're connecting through a valid point for less than four hours (domestic) or 24 hours (int'l).