The easiest way is to contact your employer and ask them for the number.
Depending on the size of your employer, a public search will not produce an accurate result because emlpoyers will use a seperate EIN number for functions such as Health Savings Accounts, Retirement PLans, and even some special business projects.
You can pay for a report from http://www.dba.com/ which will give you all EIN's associated with your employer.
Or you can enroll in this site to find EIN's associated with your employer: http://www.einfinder.com/faq.asp
some states, have a source for finding EIN numbers by looking up the company in the Attorney General's data base or your states business portal. Not all states include the EIN number.
The IRS will not tell you the number because, like SSN's, the IRS treats this as confidential private information, and will not tell you.
If your company is a public company it is easy to look up by simpy looking up their annual report as filed with the SEC. If it is a publically traded company and you give me the name of the company I can look it up for you.
If you give me your state, I will find the link for you to look it up on the state provided lists.