Astronotus ocellatus, (Oscar - Albino Form)
The albino form of the Oscar has been available for purchase in the aquarium fish trade for many years now. So no, I wouldn't say that they are exactly 'rare' or hard to find.
Is there a reason you would consider the one shown in your picture, to be rare or something?
Albino Oscars are not rare, I would say they are less common. More common is the Lutino, where you see hints of grey or darker colors in the fins. From your photo, I call that fish a Lutino Oscar. Tip for these fish... They are very light sensitive and too bright or too much light will damage the eyes. Keep the tank dim at all times