ENSO Record since 1525 Study²:
ftp://ftp.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/gergis2009/gergis2009enso.txt

2000-Year-Based Southern Oscillation Reconstruction (55 A.D.–1955 A.D.)³:
ftp://ftp.ncdc.noaa.gov/pub/data/paleo/contributions_by_author/yan2011/yan2011soipr.txt