Are you having trouble getting them locally, I know some of the chain stores only carry a few sizes. Whenever I have ordered a new die from Accuquilt itself, I generally get enough mats to get free shipping. I have heard of some people cutting done the big ones to make smaller ones. I would think it might be hard to find replacement mats as you would have to have the same thickness and density as the cutting blades are hard on the mats. I try and change the position of the mat when I place it on the die just a bit to try and keep a groove from forming especially on the strip dies. Quilt in a day, sometimes has mats on sale I believe.