Who do I contact for a UPC or an EAN company ID?

In the US, go to GS1 US for a UPC company ID:
http://www.gs1us.org/

In China, go to GS1 China for an EAN company ID:
http://www.gs1cn.org/

For other countries, go to GS1 International first and then select your group for an EAN Manufacturer's ID:
http://www.gs1.org/contact