'Wanting' means deficient or lacking and 'find' here means decide or judge , as when a jury is asked 'How do you find? Is your verdict guilty or not guilty' or a magistrate says 'I find the case proved'. ('To want' originally meant 'to be lacking or missing' and only much later did it come to be used for 'to need'. )
To say someone is 'found wanting' is to say that it has been decided that they are lacking in some quality or qualities. If someone is not up to a task, not up to the job, we may say 'he was given the job but was found wanting' meaning that it turned out that he was not capable, not good enough, lacked the necesary qualities to do it properly: his skills were wanting.