Use the "I lost my license key(s)" button to have your details resent to your registered email.
There is no such thing as a working, free AirServer license key for the current version. Attempting to find one exposes your computer to identity theft. airserver license key
Once purchased, your key is sent via email. If you ever lose it or need to move it to a new computer, you can use the AirServer License Management tool : Use the "I lost my license key(s)" button
If you'd like, I can help you compare the different license tiers (Consumer, Educational, or Corporate) to see which fits your budget. airserver license key