We need your help!

We are looking to create some new toadstool seats for our library and early years classrooms using cable drums. We have kindly been donated all of the cable drums we require, the material we need and the expertise to make the cushion tops. However, we are looking to see if anyone has access to, could donate or would be able to point us in the direction of where to locate (cheap) cushioning foam which could be used on the seats. Please see below a photo as an example of what we are looking to create. Any help would be greatly appreciated!