If no results are coming up for your chosen dates, there can be a number of reasons for this. Lessons sell out, or schools don't run lessons at certain times and these are the main reasons why there will be no results showing.
In the low season (i.e. not school holidays), ski schools will limit lessons as there isn't enough demand. In this instance you're best looking at private lessons as an alternative. Just a few private lessons could get you up to the same level as a whole week of group lessons!
If you are travelling at a busy time of year such as Christmas or school holidays, many of the lessons get fully booked months in advanced. Ski schools will do their best to have extra instructors available to accommodate more group lessons. However, keep an eye out for afternoon or lunch time lessons as these tend to not get booked up so quickly.