UCAR keeps many archives of weather data at http://rda.ucar.edu To get access, you must register your Email as a login to the site. After that, you can get access to, eg: FNL files.
FNL files are downloadable from http://rda.ucar.edu/datasets/ds083.2/index.html (but note that this path might change and you may need to browse to the location). The files are in the ds083.2. Follow the instructions on the web pages to download the FNL files. You can use a script (requires wget) or download a tar.gz file.
Don't forget to set up internet access from whatever machine you're downloading files from. At the time of writing, direct internet access from a browser or wget using the internet enabler seems not to work. It's necessary to use a proxy server, by setting this up in your browser or alternatively set these environment variables before running the UCAR-supplied csh script:
export http_proxy=" "
export https_proxy=" "