Ultimately aren't all Biels from GFF? No one else has legally imported them. Rarebreedauction.com has some nice birds.
The original latest imports are from GFF but private breeders have been experimenting with cross-breeding which is why I would prefer going to GFF directly or like Omega Hills that are breeding from GFF stock. It's the only reason I recommend them. I'm sure there are other breeders on this thread that are keeping their breeding stock un-mixed but I don't breed so can't say who has pure breeding stock.