Hi Gennaro, I haven't worked with Commerce very much, but you can try
to find
sortbale fields and add the Sort to the Search > Sort widget.
So, is "availability" an indexed field? If it is, and if its
data type is sortable (see the linked documentation), you can add a
sort option (see the same linked documentation).
But there's also a Commerce > Sort widget. I don't know anything
about it, but maybe it supports your use case.
