I know there is a silicone mat available but I am not sure who sells them. I use the silicone treated parchment paper, and it works great for me. This is the place where I buy mine from
Matfer Bourgeat EXOPAP - Parchment Paper. Its actually fairly cheap as these are the large 23 1/2 x 15 1/2 sheets, so if you are doing smaller designs they can be cut down to save on the paper. But its still fairly cheap for 500 sheets, that are good for 2 to 3 uses. These sheets work great for leaving a matte finish.