The H.15 historical data is available through the Data Download Program at:
http://www.federalreserve.gov/datadownload/Build.aspx?rel=H15

This series, H15/discontinued/RIFSPPCUS_N.M, is available at:
http://www.federalreserve.gov/datadownload/Output.aspx?rel=H15&series=9d6af117b4ad935d216722570f08f818&lastObs=&from=&to=&filetype=csv&label=include&layout=seriescolumn