Pres man,
Both links are the same.
IIRC both in the game description and mythological description, rocs resemble eagles, just are simply enormous and usually white.
I'd look for eagle or giant eagle minis and paint it white. For giant eagles, you might not get smaller than L size (while ordinary eagle minis will be too small, at least at 28 mm scale), but if it eventually will grow to L, then that might be okay for the long run.
You could also look for toys (like the Safari toys pres man links to) for eagles that are larger than 28 mm scale that would work for an M size creature (Safari has an eagle in its river toob that might be right for M, although it might also be too big. It's hard to tell.).
Google "Papo eagle" and see if those suit you. Papo, Safari and Schleich all make a variety of very nice pre-painted plastic animal figures. Larger than 28mm, a lot of them sub well for dire or giant versions of the creature.