Yes, I think they are less than $10.00 at Wal-Mart, Academy etc. You can probably also get something at Home Depot. Any kind of foam pad would work. Raising the point of contact by 1/2 inch or so makes a lot of difference and if you need more might be able to work another piece in. I anchor the cartridge holder before inserting the foam by slicing a small hole in it so the sling nut sticks through the bottom.Dillo, I assume you mean those blue sleeping mats?