If it's the woven mesh stuff that looks like a tarp, you can buy it in rolls at an RV dealer or at an RV parts vendor. There is a name for it and I can't remember. Some googling would probably find it.
Gil & Deb & Dougal the Springer Spaniel
2014 KZ Spree 262RKS & Ford F250 supercab V10 4x4 LB