I purchased one from my sewing machine store. It was REALLY expensive. I find that it slows me down. The edge of it gets caught on the quilt as I move it around and I spend a lot of time unrolling it from under my quilt to avoid having it stitched up with my quilt.
I've found that I much prefer putting a layer of Glad Press and Seal. It slides so nice. Just remove it after a day or two, so the sticky stuff doesn't stay on your machine.