In order for your company to print U.P.C. (Universal Product Code) barcodes (UPC is also known as GS1.), your company will need to become a member of the GS1 US (formerly Uniform Code Council). When you become a member, your company will be assigned an identification number for your company's use (company prefix). You will need this number to create your own U.P.C.s.
You can visit the GS1 website here to get a UPC code.