On August 8th, right before when the server restarted I got a King's Rock but when I went back after the restart, I didn't have it anymore, so I was wondering if that was a glitch or something.
If it was right before a restart you can use items that you got just seconds earlier. Unfortunately, there is no way for us to give you your kings rock back, as we would need proof that you actually got one, and lost it. Which is pretty much impossible.