BEA in general and Industry Accounts in particular, receive much of their data from the Census Bureau, and those data are often aggregated for publication purposes. If you need more detail, the economic census is a good place to start. The 1997 and 2002 Economic Censuses are available online at http://www.census.gov/econ/census02/. In addition to the Census Bureau, a variety of other data sources, public and private, are used to construct the benchmark I-O tables. For more information see Tables A and B in the October 2007 Survey of Current Business (SCB) article titled “U.S. Benchmark Input-Output Accounts, 2002,” which is available at http://www.bea.gov/scb/pdf/2007/10%20October/1007_benchmark_io.pdf.