Jim,
I had to replace the foam in a couple of quivers and used some of those yoga bloks from Wal-Mart. They are about 4x10x6 or so. They are pretty cheap and the foam is really dense, almost self healing. I have enough left over to make a about a hundred foam headed poppers for my flyrod as well.
I could only find blue, but spray painted the surface that would show and it worked fine.
From your post, it sounds like you need a form to have the quiver made. Could you shape the form from wood, making it to your exact specs, have the quiver done them shape the foam?
OkKeith