Archived (not real time) RUC GRIB data is available from the ARM (Atmospheric Radiation Measurement) program in the Dept. of Energy. They have isobaric GRIB data starting April 1998 and native GRIB data starting Dec 1998.
You can request limited amounts of data by sending email to email@example.com. Posting a message to the RUC forum doesn't go to DOE/ARM -- you must email them directly!! There are limits to the size of the data request. Tell them what you want - analyses and/or forecasts, time period, hybrid/native and/or isobaric.
For more information see
http://www.arm.gov/xdc/xds/ruc. Thanks to Laurie Gregory at Brookhaven Natl. Lab for this information.