I went through the same thing here, and let me tell you, don't bother looking for the actual foam piece.
I've searched the internet, auctions, local and far off junkyards, and even car shows and swap meets. Nothing ever turned up.
I had to take the existing one out of mine, which was literally cracked in half, with the corners broken off.
I managed to piece it back together with duct tape, and have it re-upholstered at a local fabric shop for only $100. It looks brand new, but only when it's in the car. Turn it over, it's a mess...
EDIT:
Not to mention, the clips that hold the liner and trim in place, they break most of the time when they come out, and I can't find those either. I'm using the half that survived mine, strategically placed to hold it up better.