Hi,
BioGPS does not store FASTA files nor are there any plugins currently available for handling those (that I'm aware of anyway). You could use MyGene.info (available as a python package, R package, and API) to batch convert your protein IDs to Uniprot IDs (it's not clear what protein id's you have). Then use Uniprot's
RESTful API to retrieve the FASTA files.
best wishes,
ginger