Keep sending them every couple of weeks you may get lucky.
You'll have better luck if you personally visit the companies and introduced yourself to director of flight operations. It's worked for a few friends of mine in the past, when things were a lot easier for foreigners in some Asian countries. Email applications are usually only successful if a company is actively recruiting and have asked for applications by email. Other than that, they are really a waste of time (both for the company you're bombarding the unsolicited application emails to, and yourself).