As noted before, the federal fiscal year can cause problems for economic analysis when converting from nominal dollars to constant dollars because the federal fiscal year runs from October 1 to September 30 and annualized rates for CPI are from the calendar year. The Consumer Price Index is published by the Bureau of Labor Statistics which also publishes monthly figures.
This table is a fiscal year annualized CPI dataset for 1977-2011. The figures are given by averaging the monthly figures from October through the following September of each year. Like the traditional annualized CPI figure from BLS, this is calibrated to (calendar) 1982-1984=100, so the figures will be close to the calendar rates and could even be used to convert between the calendar and fiscal year, if necessary.