Wouldn't this suffice?
wget ftp://ftp.ncbi.nlm.nih.gov/refseq/release/complete/*.faa.gz
From: ftp://ftp.ncbi.nlm.nih.gov/refseq/release/release-notes/RefSeq-release69.txt
The data that comprises a RefSeq release are available in several file formats, as indicated by the format component in the file name:
bna binary ASN.1 format; includes nucleotide and protein
gbff GenBank flat file format; nucleotide records
gpff GenPept flat file format; protein records
fna FASTA format; nucleotide records
faa FASTA format; protein records
The comprehensive full release is deposited in the "complete" directory and is available in all file types.
Thanks for that!
For combining the files I did these commands in the Terminal (mac):
If you were not restricted to RefSeq, you could download such a single faa directly from Uniprot: http://www.uniprot.org/downloads .