http://swscan.apple.com/content/catalogs/others/index-10.11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog
and betas
http://swscan.apple.com/content/catalogs/others/index-10.11seed-10.11-10.10-10.9-mountainlion-lion-snowleopard-leopard.merged-1.sucatalog