Coleman Cable has a 10,000 ft minimum order for 12 gauge and 15,000 for 14 gauge. No response from Pacific Cord as of yet, they are somehow a division of Leviton.
Try TMB in California. They do stage cable all the time and have a fairly small minimum. They make SOOW and SJOOW as well as others. They'll even put on what ever connectors and cable length markings you want. Custom cables are their main business and their quality is stellar. http://www.tmb.com