Free certificate of origin forms are available online through Shipping Solutions and export.gov. Since countries have different export documentation requirements, the sites offer forms based on the country of origin of the exported goods.
Shipping Solutions offers a generic certificate of origin accepted by most countries that may be customized by exporter, importer and country of origin. This site also provides a NAFTA document for use by exporters and importers in the U.S., Mexico and Canada.
Export.gov also provides a generic certificate of origin, as well as links to certificates particular to certain countries. The site also details the requirements for documenting origin in select countries.