Waterproof play yard fitted sheets??? Why does no one make them?

I went to register for my third (and final) baby shower yesterday and as long as I have been going to Babies R Us I have been looking for waterproof play yard fitted sheets. I soon found out that although they do make pads you can put down in the play yard, they do not make fitted waterproof sheets for the play yard. I found this very strange considering babies spend a lot of time in their play yards. Both my kids napped in their play yards as well as played. They also slept in them when staying at a family members house. Any diaper over flow or spilled milk was soaked into the pad and in a few days it was stinking up the whole playpen. I tried surface cleaning the pad but it was pointless. I have bought several Carters fitted sheets but even though they are pretty and do fit well, they do not protect the pad. This time around I actually registered for a new playpen, a Chicco, with a washable pad. I have never had a Chicco playpen but I am hopeful it will be exactly what I am looking for.