N.P.
I would not trust ANY mattress but one from that company. Try calling Graco and seeing what they can do for you. But chances are if you need a replacement mattress it's time to buy a whole new pack and play. That's probably cheaper then a new mattress.
And please do NOT put a different mattress in there. It is a suffocation hazard and it is NOT SAFE. I have read stories of this being done and kids dying.