I can't put links to casino sites in this answer but I was able to quickly use Google to find all of Harrah's casino ID numbers across the country directly on their websites. Otherwise, your best resource is going to be an internet search.
They should also have a mechanism to provide you with a replacement or give you contact information to their tax processor who produced the form for a replacement.
First, call back and try again because technically these numbers for businesses are public information, so there isn't a legal reason they can't give you the Federal Tax ID number over the phone (it might be a company policy, but maybe you can get a supervisor who is willing to make an exception).
