I googled this particular rubber and came across the tutorial linked below- they also sell the rubber, though it's very expensive.

Have you thought about just using silicone? Walmart's Mainstays brand of silicone works well to make molds and would likely work as a texture mat. It's only $2.37 (USD) for a large tube. You could do it in several layers with a layer of cheesecloth sandwiched in there for added strength.

Nancy

Thanks Nancy I will give that a try. I thought it might.