A good place to go is here:
They are undergoing some changes and may not have pre-decoded .gem
files much longer, but they will continue to have the raw grib for each
forecast hour which you can pipe to dcgrib. For today, you can go to
the links below and get the 12Z NGM and 12Z ETA. If you want some
scripts to go out and get the pieces and stitch them together (recommended
since the .gem files might be going away), let me know and I will send
them to you. This is how I get the MRF1x1 and AVN1x1 here and at NSBF..
NOGAPS at NSBF as well.
Links for todays GEMPAK files for NGM/ETA: