Better yet, read the Annual Report for the company. In most cases you will be better received by investor relations people if they feel you are more knowledgeable about the company. Most Annual Reports will also give the number. In many cases, this number is the main switchboard number for the company. When the call is answered, ask for the investor or shareholder relations department.
Most larger companies have a separate department that handles shareholder relations.
Some smaller companies handle this through the finance department or even the CEO's office. Don't be intimidated by who answers the call. More and more companies are providing e-mail addresses to correspond with investor relations. It is a good way to correspond. This is especially true if you are requesting data.