How come the godfather is so rare?

I played godfather on PS2 and loved it. Then I find out that they made a special edition for PS3 The Don's edition. Extra missions and all the DLC apparently. I've not been able to find it as a hard copy game. I found one disc for sale that doesn't work but no clue why so I'm hesitant to buy it. Does anybody know why they're so rare? I figured with it being a greatest hits game it wouldn't be too hard to find a copy but I keep striking out.