Call the US State Department and ask how you can obtain an International Driver's Permit (IDP). They will be able to direct you to the people within the State Department that are responsible for issuing an IDP.
Contact the local AAA office in your town. They are authorized by the US State Department to issue IDP for travelers that are at least 18 years of age and have a valid Driver's License. They require 2 passport size pictures and they have the forms to fill out at their office.
Communicate with the American Automobile Touring Association about obtaining an IDP for your trip abroad. They are also licensed by the US State Department to issue IDP's. Their main office is located in CA but have offices in other parts of the country.