If it is showing actual flight numbers with a price at the bottom XX miles and YY cash for VS fuel surcharge and taxes that means there is availability.

If you are getting a calender with radio buttons that means at least one of your dates is not available- but don't use the radio buttons to select the dates you want make a note of them and go back to the flight search page and enter those dates - otherwise it comes up with an error message (VS know of this error yet don't appear to want to solve it!)