How can I get an extra copy of the key for my safe?

You can ask a local locksmith to make a copy if you still have a key.

If you lost all your keys to the safe, it will depend on whether your door is open:

1) OPEN door - you can replace the entire safe lock with a new lock that will usually come with 2-3 keys.

2) LOCKED door - no easy solution. A professional would have to either pick the safe lock (not easy!) or break into the safe to recover any valuables by cutting a hole or breaking the door open with a crowbar. The exact approach would depend on the security level of your safe but the safe will be destroyed and you would have to replace it.