Hamuy Spectrophotmetric Standards [2] - Southern Hemisphere
Massey Spectrophotometric Standards [3] - Northern Hemisphere
Links
[1] http://www.ctio.noao.edu/noao/content/spectrophotometric-standards
[2] http://www.ctio.noao.edu/noao/content/Hamuy-Spectrophotometric-Standards
[3] http://www.ctio.noao.edu/noao/content/Massey-Spectrophotometric-Standards