SmartKey or regular fob?
Either way, you can buy a new one (blank) online or at dealership.
However, you have to program it at dealership.
Some website might be able to program it. However, I don't know any.
See if anyone else knows.
If you have two working keys, you can program the 3rd yourself.
This is to prevent whoever gets ahold of your key temporarily (such as vallet guy) duplicates
one to gain access later.