No clue about the original F2A devices unfortunately. The link I posted above is the only place I know of to get a F2A Ultra, though you'd want to email them first to make sure they still have them in stock and aren't lying on the website.
The only real appeal I see in getting an old F2A cart nowadays would be to use Pogoshell on its native device or to use the DS-side F2A flasher that I can't remember the name of at the moment. The F2A carts were actually woefully underfeatured from what I understand, which is why Pogoshell became such a godsend for F2A users, as it gave them decent save management and a cool plugin system to expand its capabilities.
Oh, and if you want to use the GB Bridge to run GB or GBC roms natively on a GBA, you'd need an original F2A cart.