Find a website IP Address

I am trying to find a way to ping a https:// (secure) website to obtain its IP address. When trying to do it by its name https://xxxxx.com it says that it cannot be found. I realize that many sites have turned off the ability to have its IP shown, but how would someone know what the IP is? We have a web filter that requires the IP address to allow a secure site, and cannot enter it until I figure it out.