The newest version of the SIPP Synthetic Beta is accessible on the new Synthetic Data Server at the VirtualRDC. Additional information, including how to request access to the data, is available at
http://www.vrdc.cornell.edu/news/data/sipp-synthetic-beta-file/.
The data is housed on the new Synthetic Data Server, set up in collaboration with the U.S. Census Bureau, and funded through NSF grant SES-1042181.