There was one small shop near West Town that I've used in the past but it's been a while since I was there. It was a fabric store and they sold foam rubber. I needed it to replace a couch cushion.
Is that place still there? Mom used to buy from them years ago. The place I'm thinking of is just past the old Sear's building on the left at the bottom of the hill.
I don't know if an individual can buy from there, but Hickory Springs in Morristown sells foam rubber cut to order. I worked at a small furniture store in Knoxville and we bought bed frames and custom FR products from there.